Those conditions will pertain, until the NFL jumps the shark, which does not appear to be on the immediate horizon. Given the ongoing escalation of pay for star players, the owners evidently believe it will persist for some time. So long as ad rates keep going up for NFL content (and there is no more premium content in the US than the NFL), the cap numbers will continue to rise.
So a $15 million signing bonus today might look reasonable 3 years from now, just as bonuses offered 3 years ago might look reasonable today. Comparing a contract from one point in history to another at a different point in history is irrelevant. You need to look at context, which I will illustrate in part 2 of my response below.
The only "code cracking" that any team can achieve is in stacking good drafts, having a sufficient number of core and star players under cheap rookie deals, while finding at least a "good" QB. The typical NFL roster, the Packers included, have more than half the players under rookie deals. Rookie contract performance is far and away the prime means to mine value, i.e., performance above cap cost.
Belichick is the only GM who has demonstrated exemption from the rule, with his draft pick penalties, revolving door of free agents, adaptation of schemes to the available talent, and some unique approaches to value propositions, such as "don't spend on WRs" while sniffing out market inefficiencies.
As evidenced in the Seattle Super Bowl teams, a good QB is sufficient if the the rest of the roster performs above their cap cost. To reemphasize, that comes down to having a collection of good players and star players still under cheap rookie contracts. Those Seattle teams represent the gold standard, if only temporary, when outstanding draft classes are stacked in the immediate past.
The key to Seattle's 2 dominant Super Bowl seasons was having 4 Pro Bowl and All Pro players still on rookie deals. In 2013, those 4 players (QB, #1 CB, ILB and SS) cost a total of about $3 mil in cap, and were still very cheap in the aggregate in 2014. That's a very rare act that is difficult to follow, especially since none were first round picks. The cost for those players jumped exponentially last season, while they added Graham's contract. The aforementioned 4 players now have a cap cost of $45 million, Graham costs $9 million, they are taking a $5 million dead cap charge for Lynch, and they just paid Baldwin (another $3.5 million jump, rising in subsequent year). And despite these exponentially increasing costs for what amounts to the same level of talent, they've lost Lynch, the intangible straw that stirred their offensive drink when he was healthy.
If you were wondering why Seattle looked less dominant last season, now you know. They could not sign the number and quality of free agents, their own or from the outside, during this off-season and the last. They'll be good, but don't expect dominance as they now pay exponentially more for key performers while those players offer the same performance as in 2013-2014, sans Lynch with Graham added.
Now lets look at the Packers escalating cap costs for the players who represent the top 11 cap hits this season:
Rodgers:
http://overthecap.com/player/aaron-rodgers/1085/
Matthews:
http://overthecap.com/player/clay-matthews/1096/
Shields:
http://overthecap.com/player/sam-shields/2614/
Peppers:
http://overthecap.com/player/julius-peppers/135/
Cobb:
http://overthecap.com/player/randall-cobb/1130/
Nelson:
http://overthecap.com/player/jordy-nelson/1
Daniels:
http://overthecap.com/player/mike-daniels/1126/
Sitton:
http://overthecap.com/player/josh-sitton/1122/
Lang:
http://overthecap.com/player/tj-lang/1136/
Burnett:
http://overthecap.com/player/morgan-burnett/1128/
Bulaga:
http://overthecap.com/player/bryan-bulaga/1092/
One thing that should jump out if you review each of those links, is that whether the contract has a big signing bonus (Rodgers and Matthews) or falls under your $15 million threshold, the affect is the same: gradual year-to-year increases in cap cost throughout the contract. Peppers is the one exception with the big jump from year 1 to year 2.
While one could argue that the escalations in cap across these contracts have just been on pace with the league cap increases, nonetheless we're looking at the same players on the whole playing at the same level from year to year, while they age in place and move toward their next free agent year where they will need to be replaced or re-signed, which I'll discuss in a bit as regards 2017.
Low signing bonuses certainly offer some dead cap protection against career ending injury or performance decline in the out years of a contract, as you point out, it is hardly a "code cracking" and it's aggregate benefit can easily be exaggerated. While there have been extreme examples where dead cap in the aggregate has been crippling, such as McKenzie's housecleaning in Oakland or the failed Philly "dream team", by in large it comes down to context and specifics. Not to put too fine a point on it, when you take comfort in the Packers ability to drop a player due to low dead cap if the situation calls for it, you still have to replace him with a player of at least the same quality for the same or lesser net cap cost to maintain overall performance, for good or ill. And as fate would have it, the guys one would have most liked to replace earlier, Hawk and Jones, happened to be guys with prohibitive dead cap anyway. When it did become manageable, Barrington happened to get injured and we saw replacements in Palmer and Matthews which should be regarded as a hot mess. Dead cap or not, you have to have those cheap rookie contracts on the bench to step in and play, which circles us back to stacking draft classes.
Over a year ago I began discussing the cap wall that was coming in 2017; that 2015 and 2016 were the prime window seasons. It took the press and this forum a year to catch up.
As of today, the Packers rank 21st. in available 2017 cap space:
http://overthecap.com/salary-cap-space/
At the same time, I don't think we need get into details once again regarding the Packers 2017 class of free agents. I believe this list to be the most troubling in the Thompson era. #1 running back, 3/5 of the O-Line, and OLBs #2 - #5, maybe #2 - #6. Half of the current Pro Bowl caliber players on this roster are in this group, along with other starters and some key rotational guys.
So, the only way the Packers can show they've "cracked the code" is if the guys still under rookie contracts in 2017 can fill the majority of these holes, while the other veterans can maintain their level of play. That's a high bar to hurdle. And that's assuming the Packers current roster is of championship caliber, which I believe to be debatable. If the rookie contract jumps are not in evidence we can take consolation in the fact that the last couple of drafts have included smart and personally engaging players, including the 2016 NFL All-Academic draft. Those are guys you can still root for in an off year if it comes to that.
Getting back to dead cap, there's not a lot of solace in being able to release a starter because you can pick up cap space in the bargain if the bench behind him is not strong.