I’ve installed the latest DSM 6.2.2. on my synology NAS 1515 server
If I want to update it with the latest version of the Plex server (manually) with the file PlexMediaServer-1.15.3.876-ad6e39743-armv7hf.spk I get the notification that this package is not supported on the platform of Diskstation or is not compatible with this DSM version (which is the latest)
I am not 100% sure, but I thought the DS1515+ has an intel atom processor, so if thats what you have I would have thought you need the intel package not the arm one.
You could try this one: PlexMediaServer-1.15.3.876-ad6e39743-x86_64.spk
ah well in that case you might need to wait for one of the synology gurus to come along…
You might want to add the server-synology tag to your post (if you can)
If you have a copy of 1.14 for synology, you could try that, the file you need for that is:
PlexMediaServer-1.14.1.5488-cc260c476-x86_64.spk
Edit:
fwiw, I just upgraded plex on my DS1815+ (and am pretty sure that is just the 8 Bay version of the same range as the DS1515+), and that worked using the PlexMediaServer-1.15.3.876-ad6e39743-x86_64.spk file