Apple doubled the Pcie ssd speed sometime early 2015, Link. I went though some pictures (mostly from ifixit) checking the SSD for MBA 2015 and MBP 13" 2014, the SSDs seem to be in the same form factor. I also believe they both use PCIe interface. So I come up with the question of if the two SSDs are swappable. It is my first time using this forum so if somebody already investigated it please do not blame me not using search.