I had 2 13s, and 2 15s, and had nothing but problems with them.
They all required the "follower trim" you read about online in order to barely allow the full capacity to be loaded. Then after short periods of being fully loaded, both 15s almost immediately started failing on the last 1 or 2 rounds out of the mag.
That being said, S&W customer service was curious and very quick to respond. They immediately sent out 4 new springs and followers (they insist that the springs are the same for the 13s and 15s), and after replacement work great.