If there is no leader to pin the backing to - you can buy clips online at places like Erica's that will hold the backing to the rail. A 15" quilt space - near the end - might be off a bit. It all depends on your batting and how wide the roll is when you get near the end. But with a 15" space you should be able to do 11" - 12" blocks with no problem. Hope you tried it out at the quilt show. Also make sure they have training and service available in your area - or online videos of how to use it.