Hello,
I upgraded from v8 to v9 and then v10.0.1. Every time the loading time of virtual machine is slower.
From 15sec in v8 it goes to 50sec in v10. 
So it is normal? the longest time is a black screen even before a boot or starting process of virtual OS begins.
During than "before" booting time CPU goes up (1 core goes to 100%), but HDD is fine.