BS; maybe only in bandwidth intensive apps, but I can't see these chipset give 15% on gaming or rendering or anything else we common mortals often do.
Or meybe they're referring to this gain on PCI-e 2.0; that will certainly boost gaming but not processing itself.
(It also seems like overkill. Since when did you hit a PCI-E bottleneck...)
The 15% performance boost does seem exaggerated, but it wouldn't surprise me if it's 5%-10%. If Intel manages to make enhancements to its memory controller, combined with the use of DDR3, it seems plausible.
A lot of AMD's performance lead in the synthetics were a result of the IMC. This is probably Intel's off-chip memory controller generation leap.
I do agree that I doubt you'll see any real performance gains > 5% in typical applications, such as games, though.