For anyone here in late 2020: This link is a pretty exhaustive look at upgrading the SSD in macbook pros (late 2013 - mid 2015) including what drives are compatible, what type of adapters work well, and what the common issues are. Obviously take it with a grain of salt as it’s just a forum thread, but it looks well researched and worked for me. I just replaced my factory 128 GB SSD with a 1 TB SSD (I won’t list which as I’m not sure it’s allowed) and an adapter recommended on the above link in my early 2015 macbook pro. Used an external SSD enclosure to partition the drive correctly, then booted the external drive in recovery mode and installed High Sierra, then transferred the SSD into the computer using this guide. Worked just fine.