FJ2ME
If you're on a PC on AFPS75 or 05 your exit dates will stand, however if you're SSC and switching to PC after 2015 then they will probably insist on a new exit date. For an OR then I'm not so sure as they may link it to promotion - which is not unusual for officers either as I had to waive my 22/44 point on AFPS75 when promoted after my 41st birthday.
Also, as Cpl Clott says, any AFPS75/05 pension will pay at the rank you retire at AFTER 2015 - not the rank you are at on 1 Apr 15. The rest will be paid on the FAFPS rate (whatever that might be!).
I hope that helps? I for one would suggest that you don't throw away an immediate pension at an option point, however, if you have an option before 2015 then you may want to consider it once FAFPS becomes clearer (for better or worse).
LJ