How you can install the Ubuntu Unity desktop on your Linux Mint 15 system.
use this command to install the Lightdm login manager; the Unity desktop and other assorted paraphernalia that goes with it. I just did this today with Mint and this worked. You need the ubuntu-desktop package installed to make use of this desktop though. But this does work. Linux Mint 15 uses the Ubuntu 13.04 packages; so you will not get the absolute latest version. Linux Mint 16 will though.
sudo apt-get install unity unity-scope-askubuntu unity-lens-applications unity-webapps-bbcnews unity-greeter ubuntu-desktop
If you do not get all of the functionality of the Unity desktop installed, then try this command.
sudo apt-get install --install-recommends indicator-applet-complete
I found this fix on this forum posting: http://forums.linuxmint.com/viewtopic.php?f=90&t=144779.