Well, first of all, ping is related to internet speed, not the performance of your graphics card or CPU. And, for what it is, Roblox uses a surprising amount of internet (FFXIV is a modern game that uses maybe a quarter of what Roblox recommends). If that's bad enough to cause stuttering to the point where you think you're running at about 10fps, I'd see what's happening with either your internet service provider or your router.
If it's not your internet, and other similar but offline games are also being hit that hard, then I'd say one of the components in your PC is failing, but I'd check to see if it's something to do with your internet first. If you've confirmed that it isn't the internet, then it could be the power supply starting to go; I'd recommend getting it tested or, if you have access to another working PSU already (maybe borrow one), see if replacing it fixes the gameplay.
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