You’re going to have to change your workflow to suit your computer’s hardware/performance.
Something to try is to create all of your crossfades, then export the entire video to a lossless format, then import and work on that.
Video editing is not a breeze nor is it as smooth as working on photographs. You’re asking your PC to render effects on 24/30/50/60 stills per second in real time. You can imagine this needs real power, right?
What are your PC or Laptop specs?