Early 2015 MacBook Pro SSD Upgrade

I would recommend shopping at OWC. their main focus is Mac compatible hardware. they also provide excellent customer support. and while on their site, you can have a look at the self install videos to determine for your self if you can perform the upgrade or wether you will want to farm it out to a professional.

Apple has several slightly different SSD models all which use the same proprietary connector, but some of those different models won't work with other model laptops even if the connector is the same. To clarify....macOS may not work if the wrong SSD is installed, but a non-Apple OS such as Linux will work just fine...so macOS knows which SSDs are meant for that model Mac, so be careful. You need the SSD which belongs to that specific model laptop which may not be easy or even possible to discern from listings.

If you decide to go with an M.2 SSD with adapter, then use the Sintech adapter as that appears to be the most compatible & reliable adapter. Keep in mind that if you have any issues with this setup, then it is all on your to figure out what is wrong since the SSD manufacturer/vendor, nor Apple will assist you in troubleshooting or supporting this configuration as it requires another third party item...the SSD adapter.

The OWC option is a drop in replacement which is fully supported by OWC so if you encounter any issues, then you have a company to call for assistance with that SSD.

Before you can use a third party NVMe SSD, the laptop must previously had macOS 10.13+ installed while still using the original Apple OEM SSD so the laptop's system firmware is updated to support an NVMe based SSD. You will also only be able to use macOS 10.13+ with this SSD since older versions of macOS don't have the necessary NVMe driver to communicate with the third party NVMe SSD.

When macOS 12.x Monterey was first released, the Monterey installer would not install if a third party SSD was installed internally as it would prevent a required system firmware update from being applied. If Monterey was installed while an original Apple OEM SSD was installed internally so the system firmware was updated, then it was possible to install a third party NVMe SSD internally and re-install macOS Monterey without any issues. I don't know if the current macOS 12.x Monterey still has this restriction or not. Just something to keep in mind.