Surprisingly, the Mid 2015 15″ MacBook Pro with Retina Display uses the exact same CPUs and clock speeds as the Mid 2014 model it replaces. The model identifier seems to be the only significant difference between the two models.
Nine months after the Late 2013 MacBook Pro with Retina Display, Apple moved forward with more power and twice-as-fast Thunderbolt 2 technology in July 2014.
Eight months after first upgrading the MacBook Pro with Retina Display, Apple moved to the Intel Haswell chipset in October 2013.
Nine months after introducing the first MacBook Pro with a Retina Display, Apple has speed bumped its top-end notebook.
Apple surprised everyone by not introducing a 15″ MacBook Air, as the rumor mill widely expected, and instead added a premium version of the 15″ MacBook Pro – one with a super-high resolution 2880 x 1800 pixel 220 ppi Retina Display.