Besides my clumsiness, the problem is also with the engine itself. Unreal Engine doesn't run very well on older PCs. The weakest PC I've tested it on had a GTX 1060 3GB, and it ran smoothly. Thanks!
It's easier to start over using what I already have from the old project. I only know Unreal, so I'll be optimizing that. I know more about this stuff now.
