LW lighting question...

Okay, I've got a scene with at 17-20 volumetric lights shining from left to right and right to left through holes in a wall. Now I was wondering which would generally speed up render times, just having one giant volumetric light on the backside of each wall or just keep the set up of 20 different lights. Anyone?

Generally one light would take less time because it doesn't have to process the 20 lights but it usually comes down to thepower of the lights and what its lighting and also what kind of lighting map your showing if there is one.