So I'm working on a painting of my grandparents, and everything went well for soooo long. But as I've painted more and more it's started to get extremely laggy. It lags while I'm painting, the layer lags while hiding them, and now it won't let my paint anymore. No matter which brush or pen I use nothing will show up.. I don't get it. I tried to open another painting to check, and there I'm able to paint, but.. I get this loading window for every stroke. And as I wrote in the title, this is a christmas gift so it's kind of important to get this done