Help, my chickens quit laying???

Is your coop large enough to leave them inside the coop and run until noon for a couple of days? You may have some that are laying away from the coop. I find every time we have a cold snap, mine will slow down, but this time of year is when they usually get cranked back up. I only provide 12 hours of light per day, and mine lay well. It's not necessary to have your light on 15-16 hours for eggs. You might try worming them, and looking them over for mites and lice since those things can cut down on laying. Also, on your next day off you might go into the coop every hour and watch to see who's in the nest boxes, since some chickens will peck and eat eggs when they are cooped up in winter too much. Also, you might add some crushed oyster shell each day on the side, in case any egg shells are thin causing eggs to be eaten. A 50 lb bag will last a long time, but they need it.