Writeup about what is different in Ubuntu 15.04 from the general build instructions.
Ubuntu 15.04 alread brings the correct version of kismet. Install with
sudo apt install kismet
Add the plugins with
cp kismet-plugins/ubertooth.so ~/.kismet/plugins/
cp kismet-plugins/ubertooth_ui.so ~/.kismet/client_plugins/
Ubuntu uses 'plugdev' as group for usb permissions. Copy them with
sudo cp 40-ubertooth.rules /etc/udev/rules.d/
Log out and in to get correct permissions. Also deattach and reattach the ubertooth.