VirtualBox 6 feels/runs/works a lot slower than VirtualBox 5.2

[Artem S. Tashkinov]

I wonder why VirtualBox 6.0 is quite slower than VirtualBox 5.2 in many regards:

• it's a lot slower to launch: VBox 5.2 launches pretty much instantly, 6.0 takes 2-3 seconds.
• it takes additional time to launch guest OSes: I see no delay in VBox 5.2, while 6.0 takes a second or two.

My hardware:

• SSD disk 500MB/sec read/write (it doesn't even matter, since consecutive launches impose the same delays when everything is cached)
• 16GB DDR3 800MHz RAM in dual channel mode
• Intel Core i5 2500
• OS: Fedora 30 with XFCE, without any fancy features like desktop compositing. I also see the same slowness under CentOS 6.x x86_64.