Is there a way to change flavours from Ubuntu 15.04 (Vivid Vervet) to MATE 15.04 without downgrading back to 14.10 first?
Ok got it , it was staring me right in the face!
First make sure your package list is up-to-date by running:
sudo apt-get update
To install MATE, choose one of the apt-get options below.
This will install the base packages required for a minimal MATE desktop
sudo apt-get install mate-desktop-environment-core
This will install the complete MATE desktop
sudo apt-get install mate-desktop-environment
This will install the complete MATE desktop including a few extras
sudo apt-get install mate-desktop-environment-extras