There wont be any immigration; with hand luggage only you would be able to walk from the gate (Generally a B gate on OS) to the taxi stand in 15 minutes.

The problem here lies in the luggage. It is summertime and the airport is busy. During low season it may easily take 30 minutes for the bags to start coming out, during high season it will be worse and I do not expect that you will be able to make it.

However if you do manage to get a hold of your checked bag on time, from that point on it is less than a 5 minute (brisk) walk to the curb.