They only open one exit, so those sitting at the back of the plane will get off last. I don't think this matters at all. As there will be planes landing frequently at the aiport there is a continuous stream of passengers waiting to collect their luggage and be processed through immigration services. Regardless of when you get of your Virgin flight you will have to take your place in this continuous stream. I've not encountered any serious delays at baggage collection or immigration at Orlando (unlike some other American airports I coud name...).
Regards
Rob