I thank you for your letter brought to me by Rayarama. Yes, 15 minutes is sufficient time for the offering to remain on the altar. You do not need to lay down Lord Jagannatha on a bed, by mantra you say my dear Lord please take rest. In temples, there are two sets of deities, the big set is always on the throne, and the smaller set is handled, taken out for a stroll, laid to bed, etc. There is no difference in the small and large set, of course.