Hard to say what will be legal in 2015, but by the 2014 Q& A,
this would be legal. Or you could send the first choice pressure switch back to Nason & asked that it be re calibrated so that it actually switches at 115 psi rising. Or order one from Nason with a 118 psi rising SP. That would keep you keep you below the about 120 PSI stated in the rules.
The instructions from Nason for recalibrating the SM series pressure switch calls for rotating the barrel 1/2-3/4 turn. Not dissembling the switch. I have done this on our tee shirt cannon & it has been working fine with a consistent set point (120psi) for the last year or so. Per the 2014 Q&A you cannot do this on your comp bot whether or not it works is a mute point for FRC. As in all things, you should always thoroughly test your adjustment to be sure they have the result you intended.