In March 2015, the 15" was still sporting the NVIDIA GT750M, plus the same battery it had from its introduction, and the Haswell CPU (which is the same it is still sporting now...).
It was already kinda old
Skylake was already rumored, so as new GPUs suitable for the MBP.
As I didn't really needed a new computer at that time, I waited for June, when Skylake was officially introduced by Intel.
But back in June, 15" MBP was "upgraded" with the AMD 370X and a slightly better battery. So I started (delusionally) hoping for an Q4 2015 Skylake release.
And it didn't happen.
Then March.
Then WWDC.
Then September Event.
And finally, here we are, october.
What a long journey...
Ok, I thought you were talking about the 13". While also not really upgraded in a while, it's still pretty good (but not at value for money, really overpriced)