It is wierd in that you asked if a grammar school in Bucks is a feeder school for Priory Rise - a primary school in Milton Keynes. That is not a sensible question. What you really mean is: can I live in MK and still get into a Bucks Grammar School?
The answer is possibly. However, The RLS works on children taking the Bucks 11 plus and getting a score at 121 or higher. This exam is taken very early in Y6. You would have to make arrangements for your child to take the exams if you do not live in Bucks. All children in Bucks are entered for the exams unless they withdraw. If you gain a place, you would pay for transport from a non catchment location.
Totternhoe is in Milton Keynes - it is not in Bucks and it is not in the catchment area for the Royal Latin School. There is no question of any primary school being a feeder for RLS. The only way to get in is to get the required score in the 11 plus. RLS allocate places based on catchment (as priority 2) and Totternhoe is not in catchment. It is not in Bucks. However, RLS allocates places to all qualifying children living in its catchment area and, most recenlty up to a distance of 8.9 miles. Catchment children are priority 2 and non catchment children measured by distance from the school are priority 6. Not living in catchment may be ok, but it is a gamble.
Exactly the same applies to Aylesbury Grammar School, Aylesbury High School and the Sir Henry Floyd Grammar School also in Aylesbury.
Therefore, decide if you want to be in catchment for one of these schools and move over the border into Bucks to be certain. Or measure the distance from RLS where you want to live in Totternhoe ,and see if, most years, you would get in. If Buckingham and the surrounding towns/villages expand, places from outside catchment will get squeezed as they are a low priority.