Reduced-pressure (vacuum) evaporation/drying of 15 liters of aqueous solution
The aspirator pump would be unlikely to be damaged by the distillate (and can be cheaply repaired or replaced), but the electric vacuum pump likely will require a cold-trap to prevent the vapors from destroying it.

The aspirator pump would seem the way to go, but you must factor in the cost of water in your location. This Nalgene aspirator uses ~6.5 liter/minute. A recirculating aspirator pump might be the best compromise for a production environment, where efficiency is important, and it might be feasible to save and recycle the distillate.