System Information
Operating system: win7 64
Graphics card: gtx1070

Blender Version
Broken: git.bf9904ec8018
Worked: 2.79

Short description of error
Subsurface modifier make switch between "object mode" and "edit mode" very slow, even with low poly meshes.
Setting the subsurface modifier UV settings to sharp give a little boost, but still very slow.
Here is 2 identical files, one for 2.79 and the same for 2.80 to check the difference in performance.
This is probably a well known issue, but may those files, that I'm actually using in production can be helpful to make some tests.

Thank you