As BOAC has pointed out - this question was specific for the 737.
There is very little (I will not say None - although it was what was taught on my type rating course) drag at flap 1 or flap 5 - as evidenced by the fact that the aircraft will not descend appreciably better with these settings - you need at least flap 10 to get any noticeable drag.
So in the circumstances asked in the original question there is no reason apart from SOPs why you should bring the flap up, although you could perhaps consider that on a flap 15 take off you might go from flap 15 to flap 5 then stay there until you get to "gear down flap 15 landing checks" on the final approach.
All that assume no performance issues (apart from the choice of take-off flap setting) as given in the original question.