You may do the below two things:
 Go to Startup-Applications from the main menu on the top, and disable all unneeded services such as bluetooth-monitor, sharing-service, etc.
(Sometimes, all startup items are hidden from view by default for security purposes. If that is the case, then issue below command in a terminal, and then open the startup applet:
sudo sed -i 's/NoDisplay=true/NoDisplay=false/g' /etc/xdg/autostart/*.desktop
 Login in Ubuntu-2D mode instead of the default one.
 In your virtual machine settings, check how much RAM you have actually allocated to your vm. It also helps to check 3d-acceleration and other settings and disable the ones you don't use.
I'm sure you will lose some of the sluggishness after you do this.