If you are still serving and are interested in topping up your AFPS15 pension, you can opt to make additional pension contributions either by way of a lump sum or by monthly deduction from salary.
Choosing to pay by monthly contribution only commits you to paying until the end of the financial year. At the start of the next financial year you simply give fresh instructions in order to renew, amend or stop your contributions.
You can start the ball rolling by submitting a quote request form (AFPS form 6) obtainable from Veterans UK
If you are on 75 and 15 you can no longer boost the 75 scheme benefits as that scheme is effectively closed to you for new accruals. However contributing to 15 will boost your benefits overall. This will be reflected in improved Early Departure Payments (EDP) – so bigger lump sum and income on exit if you serve beyond your 20/40 point and ultimately lead to an improved AFPS15 pension.