Doing a little binary search on Everymac, it seems that the last new MBP model with Nvidia graphics was mid-2014. Both offerings with discrete graphics from mid-2015 had AMD cards. I'm also fairly sure you could still buy those mid-2014 MBPs well into 2015; I distinctly remember seeing both AMD and Nvidia MBPs available in the online store around that time.

http://www.everymac.com/systems/apple/macbook_pro/specs/macb...