There are a lot of posts and several threads about this issue - search for ‘slow selection’. It seems mainly to be caused by:
- always slightly dodgy OpenGL support for the common Intel integrated graphics chips used in many laptops
- out of date graphics drivers (or sometimes driver updates that ‘break’ previously working drivers)
- some Windows 10 updates that break the OpenGL graphics chain
- using the built in graphics instead of separate graphics card where a laptop has one of each
SU isn’t the only program to suffer from the Windows updates, but it seems to be a common cause of problems for SU, judging by the volume of forum posts about it.
SU 2017 suffers from many of the same problems, for the same reason - inadequate implementation of what SU now requires - good drivers for OpenGL 3.0 or better.
There is a fix for SU2018 (not applicable to 2017), which worked for me on an old HP laptop with Windows 10 and an out of date Intel HD 3000 chip.
See potential fix