With a 5.5t motor I can get 2 five minuet races in with a 5400mah 50c,
http://www.m-k-racing.com/product_in...oducts_id=8698 this is a great lipo. My stepdad has the saddle version but they are the same specs. We only do 2 races to make sure but im sure it could do 15 minuets. Have you got a 'smart' charger? if you dont you will need
http://www.m-k-racing.com/product_in...oducts_id=8925.
HTH
Sam