There's one when you use the Fire Hose in the Hydrant. You need to be super careful to not activate the ending of the demo. Above a vent to the left of the door.
Nice ok, that's 16.
A couple places I'm surprised I haven't found any:
- Subway car control room
- Below the alleyway fire escapes (area between the shortcut ladder and the apartment w/ the safe)
- Safe room in the Donut Shop
- The literal Toy Uncle shop
- The shop with the broken windows near the subway entrance