officially 1515+ can’t get DSM 7.2 or above. DSM 7.1.1 is the last supported DSM and it is now end of life cycle.
but…!
https://github.com/prt1999/Synology_model_upgrade/tree/main?tab=readme-ov-file
yeah, i didn’t try it yet lol
just in case, it is backup… visit above github link