The email I have a copy of says that in your case you will get 4.8 years of PA supplements.
Just to clarify, as I understand it, AFPS 75 is not a final salary scheme. If you leave at 55 your pension consists of a basic bit, the same as a blunty Flt lt who serves for the same number of years as you, plus so many years worth of PA spine supplements which ensures you get an enhanced pension for being a member of the master race.
In the case of the pension switch over, you get to bank the supplements you earned on AFPS 75, but you must still serve 5 years from going onto the spine.
I'm certainly not an expert, but I reckon in your case, with 4.8 years done, your banked pension will be almost identical to a mate who leaves the RAF today having done 5 years on the PA spine.
Given that Apr 15 is the earliest that the change will happen, I don't think you have much to worry about.