Hi, yes, originally I had everything hidden in my original project. Then I created a new project (the one I uploaded) to demonstrate the issue, but forgot to make things invisible. You can try yourself: the performance is the same no matter if things are visible or hidden. In my case with an Intel i5 and a GTX 1060 it’s 4 FPS.
In case you didn’t notice, I updated my post earlier with the solution which was to lower the Resolution Preview U value in each curve. Originally I thought it was a problem with Blender 2.8, but then realized the problem was the user