SQL Server Management Studio (SSMS) is way too slow in its GUI
I also had the mystery slow down in v14 and then upgraded to 18.5  Post upgrade 18.5 worked fast...a few days (and reboots)  later it bogged down again. Network trace showed a ton of IP6 traffic which we have not configured but somehow became a default 'on' in Windows 10.  

Disabled Ip6 on the ethernet adapter and all working fine now.