what software do i need to operate scansnap s1500m using Sonoma 14.7

Sometimes another ScanSnap driver that is compatible with that version of macOS may work, but I don't know which one that could possibly be. Just do a general Internet search to see anyone has posted that information.

Actually while trying to find the ScanSnap website I stumbled upon this Apple forum post as one of the top hits:

ScanSnap 1500M on MacOS 15.1. - Apple Community

Another possible option is to see if VueScan is compatible with that scanner.

Vuescan supports the Scansnap s1500m. I can vouch for how good Vuescan is; I have been using it for many years with different scanners & Macs. You can get it for $49. And you don't need any Fujitsu drivers or other s/w.

But the $149 Professional Edition is totally worth it. It includes lifetime upgrades (not just updates, but full upgrades) and it supports hundreds of scanners.