If you serve until the Immediate Pension (IP)point you will get an immediate pension and pension lump sum reflecting the amount of service you had completed up to 1 April 15 but based on you rank at departure. You will also get a deferred AFPS 15 pension payable at your state pension age.
I am assuming that you are an officer so, leaving at IP will not entitle you to anything from the new Early Departure Payment Scheme (you have to serve at least 20 yrs and be at least age 40).
If you are a Forces Pension Society member David Marsh and Anthony Henderson will be happy to give you personalised figures.
www.forcespensionsociety.org.uk