Originally Posted by Manning-is-my-hero
I have the 15 and its not too long when you through a t-stock on there. It doesn't get in the way and, like others have said here, allows you to use a whole 10 round tube and still have a few balls in the tube in case you need them.
It depends on how long your arms are and the position you have your T-stock in. With mine on my T-stock the end cap of the 15 round tube is about an inch away from my mask lens which I don't find comfortable.