I have a 2 core, 2 thread, 4gb RAM 3855u Chromebook that I installed Plasma on, and it's usually pretty responsive.

I have not, but also it's not slow immediately, it takes time under use to get slow. Fresh boot is quite fast. And then once it's slow, even if I close my IDE, browsers and everything, it remains slow, even if CPU usage is really low and there's theoretically plenty of memory that could be freed easily.