Här finns info om skillnaderna, de verkar vara den del hårdvarubyten etc
Mid-2015 & Mid-2014 MacBook Pro Differences
The "Mid-2015" MacBook Pro models are quite similar to the "Mid-2014" MacBook Pro models replaced -- the MacBook Pro "Core i7" 2.2 15" (IG), "Core i7" 2.5 15" (IG), "Core i7" 2.8 15" (IG), "Core i7" 2.5 15" (DG), and "Core i7" 2.8 15" (DG). Both lines even share the same "Haswell" processors.
The most notable differences between the "Mid-2015" models and their predecessors are that the "Mid-2015" MacBook Pro models have a more advanced trackpad, faster flash storage, and a higher capacity battery. The higher-end "Mid-2015" models have modestly faster graphics than the predecessors, as well. However, because the models are so similar, identifiers are particularly important for differentiation and the similarities are well worth evaluating in-depth, too.
LÄNK: https://everymac.com/systems/apple/macbook_pro/macbook-pro-re...
Beror alltså på vilken version av 2015 du har.