iPhone 15 Pro keeps losing eSIM signal while others on the same network work fine

Have you contacted your Carrier ?

(Although few relish the prospect of contacting any carrier)

Your carrier is after all, the entity providing the problematic “communications link” - including actually provisioning the eSIM “inside”

your phone - and so are in the best position to initially troubleshoot these sorts of technical difficulties.

Sometimes one needs to “dig a little deeper” with carriers; to get past a carrier’s Tier1 “script reader” support reps.

(Just the unfortunate reality of modern tech support)

One needs to be their own strongest advocate.