Apple uses a custom SSD design. Review this IFIXIT guide: MacBook Pro 13"" Retina Display Early 2015 SSD Replacement You can see the physical difference between them.
Your choices are either finding an Apple SSD on eBay, Amazon, or a 3rd party which offer a SSD designed to work in your system: Transcend - JetDrive 820 or OWC - Aura SSD"
"Im using a 1tb WD black SSD in my MacBook Pro 15” (mid2015) using an adaptor bought off amazon and is working absolutely fine……
Update (12/06/2018)
the adaptor is Baoblaze 12+16pin to M.2 NGFF M-Key SSD Convert for Macbook Pro retina 2014 2015 MF839 MF840 and the ssd is WD Black WDS100T2X0C 1 TB High-Performance NVMe Internal SSD"
