In terms of the crew numbers, the only thing holding back service on the LCY-SNN-JFK leg is that after the SNN stop is the time taken to set up the video players which can be fiddly. I use my own laptop so I just waive them by.

Do not board the plane straving as your main course is served aften the SNN stop and after the video set-up and and after a drinks service. I have never had more than 12 pax on the flight and sit near the front so service is fairly fast anyway.

You do get served drinks and you starters/canapes between LCY-SNN but that is hardly filling.

On the flight back, its a night service so most pax tend to sleep asap. Should not be too demanding of crew.

Crew already overnight in LCY prior to the flight so I am not sure why they would want to to overnight in SNN; unless the SNN allowances are more than LCY or it is a nicer hotel. I think it does matter for pax to see the same crew all the way on this flight (re: drinks orders and requests). A change of flight crew is less obvious to pax except for the announcements from the cockpit.