OS X host UI slowdown during Linux guest usage

[osx-user]

I am using VirtualBox on my OS X laptop since VirtualBox version 4.3.

When I updated my OS X to El Capitan I had to update VirtualBox to version 5.0 too (because vbox 4.x didn't support El Capitan when I applied OS X update).

Since my update to VirtualBox 5.0 I noticed that OS X User Interface (UI) slowdown in time during active guest usage.

First few days all looks OK, but after one week of active guest usage (my guest running CentOS 6 x86_64 with X Window System + Gnome, with VirtualBox guest utils) host system UI slowdown to unacceptable level. All OS X graphical effects lagging.

If I have little usage of my Linux guest, host system may slowdown very little - 1-3 weeks host may work before visible slowdown.

If I stop guest or suspend it and start again (without OS X restart), system will go back to normal state and slowdown will begin accumulate again.

One week ago I updated to Virtual Box 5.1, apply all available updates to OS X, update VirtualBox guest utils in hope to have no slowdowns. But it still happened again.

I had installed in my My OS X host: VirtualBox, Skype, Adium and nothing else, I use Safari very active. Linux guest has installed CentOS 6 with Graphical Interface, nothing special - I am using only gnome terminal + ssh.

[osx-user]

I'm using USB flash passthrough from host to my Linux guest.