not really.. the idea is to have enough filtration to remove solids.. you can accomplish the same thing with powerheads but for a 15G tank it prob won't be needed.
most of my tanks(actually all of them) are over filtered..mostly to keep good water movement.
it depends on the tanks really and the filter placement.
a 20 log for instance would benefit with 2 smaller filters one on each end..that's the logic of it anyway.
