A friend of mine gave me one of his old comps to use until I could get an actual setup. I've used this comp before so it had TB installed already. It ran one of the older versions, 4.82 I believe, really well 60+ frames no matter what. But when I updated TB to the latest version the frames suddenly almost never go above 15. Even after turning all the settings down to the minimum, turning the newmenu off, shutting down every not needed process on this comp and even updating all of it's drivers it still never seems to go above 15 frames.

That's some really old hardware, I actually doubt you could get 60 fps on first gen i3's integrated graphics.
Try disabling all effects if you haven't already (including 3d items, hairs, flames and trails), if even that doesn't help there's not much else you can do.

oddly, on my high end setup, "minimum" graphics settings yields much more poor performance in comparison to high. try going on high, then disabling things like ray tracing, models, effects, et cetera. if that doesn't help, bump down the graphics setting and repeat until it does any better. couldn't tell you why my experience with the settings is weird, but that's how it is for me.

I would most likely do as the others suggested work your way up the graphics to fin a happy medium. If you still get 15 no matter what settings that would be a problem. With your hardware it looks like you could probably run medium and maybe high