With all the $ we have guaranteed to Rondo, KG, Bass, Green, Jet, and Lee we are probably already over the cap for next off-season. If I am correct about that, then the only way we could sign any FAs is with an exception. So, if Danny can get Paul to take a pay cut it might make it easier for us to extend AB's contract while staying under the luxury tax (so that we can use the MLE on a FA), but it won't allow us to make any real moves.
I do not think the Captain's play is worth 15 m, but I would HATE to see Pierce on the back of another team's uniform. Ray Allen was one thing; Paul would be another.
I know PP has said repeatedly that it's not about the money, so if taking less would allow the Celts to use the MLE he might be willing to do so.
In reality, I don't think it will matter and we'll happily pick up that team option. Pierce is significantly better than any player we might get with the MLE, and cap constraints mean that we won't be able to go out and use the 17 m from PP's deal on another player of equal caliber.