Since Apple uses a proprietary SSD connector you will need to use an enclosure that has the same proprietary SSD connector. OWC Envoy Pro Enclosure is the only one I know about. Very few vendors make them because there is such a small market for them. Sometimes OWC will have a used or Open Box enclosure for sale at a significantly reduced price.
If you use a standard M.2 SSD you will also need an SSD adapter. The Sintech adapter is the only one which seems to be reliable. I have no personal experience with using a standard M.2 SSD and Sintech Adpater on a Mac. My knowledge is from reading lots of posts on these forums. Keep in mind that the M.2 SSD vendor will not assist you if there are problems with the SSD while it is installed in a Mac as that is an unsupported platform. You do this at your own risk.
If you are going to install Monterey, then keep in mind that at this time you will first need to install Monterey on this laptop while the original Apple SSD is installed internally in the laptop. After Monterey updates the laptops system firmware, then you should be able to install a third party SSD and install Monterey (in theory).
I highly recommend keeping the original Apple SSD in case it is ever needed to install a system firmware update or to troubleshoot the laptop and the new SSD.
You should always have frequent and regular backups. It is impossible to recover accidentally deleted data from an SSD after the Trash has been emptied plus an SSD can fail at any time without any warning signs (even a brand new SSD).
Also you mentioned "memory". Memory and storage (SSDs) are two totally different things. Memory on the Apple Retina laptops is soldered onto the Logic Board and is not removable. For the 2015 laptop, the SSD storage is removable.
https://www.crucial.com/articles/about-memory/what-is-the-difference-between-memory-and-storage
