Hi, have a macbook pro retina 15'' from 2014 with a 512gb SSD which has a healthy speed of around 850mb/s. Now my 2015 13'' 256gb SSD has speeds that reach even 1.3gb/s (saw 512gb models that get even more!) Is there anyway to upgrade my 15''? It seems none of the third party manufacturers have upgrade options and all I found were eBay auctions which I'm not sure if they're 2015 models or not. Cheers!