Well, the current 15 inch MBP is running 2 years old Haswell processors, so it's simply a bad buy when Skylake MBPs are coming out in a few months.

Additionally, Skylake brings DDR4 memory, Thunderbolt 3.0 (Thunderbolt over USB), and better performance/battery life. There's also possible wireless charging support, and the Skylake integrated GPU possibly has double the speed of the Haswell Iris chips.