I'll expand on Hunter's comment by going Dr. House style and making some ridiculously specific assumptions in painting my theory
I'm going to say that your 15ft estimate is because you had a ~15ft leader tied on with a albright knot (or similar). With those knots it's critical that you tighten primarily by pulling on the leader and the tag of the braid only. If you pull hard on the main line of the braid before the knot is tight you end up with a weak spot in the braid right before the knot (at least that's what Grandpa told me, others can feel free to correct me if I'm wrong).
If that's actually the case you can either adjust how you tie your knots or switch to a swivel and shorter leader. Personally, I go with a swivel anytime I'm tying a knot on the water, it's more forgiving and I get a little queasy if I focus too hard on a knot in my lap while on the water.