The early 2015 13" MacBook Pro and mid 2015 15" MacBook Pro are upgradeable. As "sfar" has pointed out the instructions are available at ifixit.com. It is a straightforward process and takes about 1/2 hour. I have done both a MacBook Pro and a MacBook Air. A SSD can also be purchased at Other World Computing. They have a kit which includes the SSD, screwdrivers, USB to SATA cable, and a transfer enclosure. If you already have the proper screwdrivers you can purchase a transfer enclosure and cable on Amazon at a cheaper price.
Adding storage to a MacBook Pro
Since diving into the world of hi res digital downloads, I have used my MacBook Pro, circa 2015, to store my music. Getting very low on storage space. For folks that have encountered the same issue, what did you do to add extra storage space? Cloud? External drive, either disc or solid state? And someone mentioned that there are those that do surgery on MacBook pros and install larger internal hard drives. Thinking of going at least 1 TB. I want to make things as easy as possible. Preconfigured for Mac would be super. Thanks in advance for the suggestions.