On most cars, 15 miles is just fine.. leave the car in neutral. The reason you can't tow a FWD long distances with the tires on the ground is that the lubricant isn't being circulated around the differential and output shaft, which is still being spun. Honda says 100 miles, Ford says 50, but I've never seen a car say you couldn't tow it 15 miles.
One solution to this problem, by the way, is just to leave the car in gear. Then the lube gets circulated. Make sure you pick a high gear (4th or 5th) or bad things will happen to your motor when it gets spun to 20,000 rpm. ;-) Also, with certain types of DC drive, you must not back up while towing - doing so can result in plugging the motor through the freewheel diodes, potentially damaging either diodes or motor or both. S.
