Curves presets make Lightroom very slow

Interesting, did not understand what you were doing, was not aware of the ability to place a preset specifically for a curve, and place the file in that directory, so that you can select it in the curve panel. So experiment. Nice.

So, do you perhaps have any presets in that folder that are broken/corrupt?

Do any of those presets apply to anything other than the curve?

Do any of those presets involve a profile? One that may have gone missing.

Maybe put the presets back in the folder one at a time, (close LrC before each add, then restart LrC, one at a time) see if a particular preset add brings LrC down.