Well you have to either leave a direct or get REALLY ugly (10 and 5), so I guess I would just play 15-7? It's the most direct attempt to make a counter-prime adn get back in the game. If you slot the 3 and he hits, you're getting doubled out next roll. If the slot succeeds, you maybe make the 3 but that's not THAT great of an accomplishment here. When you slot the 7, you at least make a huge improvement when it works
If this play leaves a direct blot on 3pt, I would just make 3pt and leave a direct blot on 15pt. At least 3pt will be made. However I am not sure I can justify leaving a direct in any case.
I like making the 3 point. We need to try to get equality for whites prime, and we need to be ready for an opportunity to make a useful hit. Let's start filling our board.
Leaving a blot on the 7 is distasteful, since it lets white run with a hit, improving the pip count and having the prime. A blot on 8 is not as bad, with only four rolls.
If we get hit on the 15, at least white breaks his midpoint while still having checkers in our board. Those two checkers will need to be nimble in extricating themselves. The pip count won't change too much. either.