Not much he could do? That was a crap kick, basically gave away the game. The 2 rail kick would have gave him a legitimate chance to make the 6 and win and that kick he played instead at that speed had absolutely no way to work well. you got him into a tough spot and the way that guy played that kick he might as well have just racked the balls and not even made you shoot.
After seeing the video and the real angles I know for a fact I would not shoot the 15 there. I would jack up and punch the 11 into the 13 on it's left hand side with bottom right hand siding gatting the cueball to hit the rail at about the diamond before the side where the right hand spin would help kill the ball behind the 14. The 12 would come out close to the side pocket while the 11 and 13 would be somewhat close to the rail still but both would go. The chances the guy would have any shot would be slim.
The reason I dont like your shot is just what happend, you overhit the safety component of it and had it horned out the guy had a duck. The shot you shot I would only shoot to make, not as a conditional safety because trying to make both the safe and the pot at the same time lowers the chance to make either. Potting the shot to make it like you did worked well, especially since the guy had no heart or brains on how to play the kick after you did it. If you know you can make the pot shooting the 11 there is a good shot.
I would play the safe with the 11 into the 2 tied up balls and hook the guy behind the 14 all day there. Seeing it on video is alot easier to judge and I knew in about 3 seconds that is what I would play, I am not shooting the 15 there ever.
<edit>I looked at it again, still shocked the guy played that. He also could have took the foul and pushed the 12 onto his 6 ball, sure you are likely to get out anyways with a simple breakout (probably by using the 6 ball to punch the 12 back off the ball and thereby re-hooking him) but he may get a easier kick then to make. He had alot of options, he took the worst shot of them all imo, he might as well have just racked the balls.