This following guide is on how to disable touchpad in Ubuntu MATE 15.04.
The default mouse and touchpad configuration on MATE Control Center is poor of feature. This will help you, just install gpointing-device-settings :
sudo apt-get install gpointing-device-settings gpointing-device-settings
Once you open GPointingDeviceSettings, all you have to do to disable your touchpad is to check “Disable touchpad” as shown below, and the touchpad will be deactivated from that point on.
Hope it will help you!