Has Rafa changed stick recently, and is it working for him?

I've heard rumors that he switched racquet - or modded it differently - because he felt like his shots weren't hurting djokovic at all (or whatever other reason). So 1) is it true that he changed racquet? And 2) What can we conclude so far? Does the disastrous 2015 season coincide with the racquet change?

I'm just curious here, thanks for helping.