Hello I found something regarding this topic.
I had the same problem as more of you have: windows 10 takes 8 minutes to boot, same with ubuntu.
I do have Avira installed and when i shut off the "Protection cloud" function/button in Avira (or quit Avira entirely), everything works as normal (even with realtime protection on from Avira) in parallels and the systems run in seconds and not minutes. So if you ask me, something goes wrong there.
I hope that this is helpfull information for you! Goodluck!