I upgraded the stock SSD to an M.2 NVME SSD on my early 2015 13" rMBP. : r/mac
How to Upgrade Retina MacBook Pro SSD Storage: 13-Inch: EveryMac.com
Amazon.com: MCE Technologies 1TB Internal SSD Flash Upgrade for MacBook Pro Retina (Mid 2012 - Early 2013) - Includes USB 3.0 Enclosure for Original Drive & Install Kit! : Electronics
MacBook Pro M.2 SSD Upgrade Guide | MacBook Pro NVMe SSD - YouTube
Sostituzione SSD MacBook Pro 15" Retina Display versione metà 2015 - Guida di riparazione iFixit
655-1857) 128GB SSD - Apple MacBook Pro Retina 13″ & 15″ (2015)
Solid state drive-SSD for Early 2015 MacBookPro | MacBookPro12,1 SSD upgrade | Flexx Memory | Free Uk delivery
SSD Drives For MacBook Pro with Retina Display (Late 2013 - Mid 2015) - Macfixit Australia
661-03563) 1TB SSPOLARIS SSD - Apple iMac & MacBook Pro Retina