Billy, I don't think the angle is there to accomplish that shot. The three would have to be hit much more full to leave the cue ball where you suggest and that will send the three well wide of your pocket. If the three is hit thinly enough to keep it in the vacinity of your pocket than the cue ball will end up more or less near the side pocket on the opposite side rail.
Either way this position will allow your opponent an easy kick back into the fifteen and more trouble. No, I think we have to find a way to turn the trap to our advantage. Anything else will only result in deeper problems.
Tom
Tom and Billy, playing off the 3ball is a touchy shot but could be accomplished by either shooting the 3ball in the top left pocket with a left of center ball hit or sending the 3ball slightly to the right of the top left pocket with the speed to position the 3ball back down table near the 4 and 14ball. Your cue ball (if struck with center left) should come off the side rail float to the top rail and spin to the left side rail in hopes to end up on or near the rail utilizing the 7ball to take away the right side rail for the return kick from your opponent. I understand that this shot has to be hit very well to get the results I described, however, considering the situation you're confronted with one should be content that the route is even there to possibly escape the trap and protect the position.
I believe coming off the 6ball sending the cue ball to the top rail right of the pocket and ending up on the side rail behind the 7ball (protecting the 3ball) would be an easier shot to execute with a more predictable cue ball.
The two shots that I described are low% shots to arrive at the optimal position on the table to protect your position, but, none the less they're there. Of course that's providing that Tom's initial shot of ticking the 8ball isn't available. Other than the three shots that have been brought up I really don't see much more you can do to salvage the position.
Dr. Bill