I had to update my cpu & motherboard from 2015 recently. It works a bit better now but it'll definitely still stutter if there's a lot of avatars around.

If you're using Firestorm it's basically bloatware at this point and whereas it's more user friendly it's way more buggy. Definitely try Alchemy viewer and see if that helps at all. It's a fairly well optimized viewer and good to have as a backup c: