What kind of 'priority handling' on the ground did you have in mind? Concorde gets all the priority handling it can at LHR these days, but if you think you could get a turnaround time below 1.5 hours with passenger changes then there are some very hard working handling staff who'd just love to meet you - and your time machine! Frankly I'd take 21 hours in first class with some horizontal rest than 15 hours sitting upright in a narrow body. Anyway, given that BA generally needs to utilise a back-aircraft to protect the daily JFK service you might find you need an in-situ back up aircraft at Heathrow, Bahrain, Singapore and Sydney, plus the one thats operating the outbound service and one operating the inbound. Thats six aircraft, and we only have five airworthy ones!