It all depends on how warm it is in the room that he is in on how much extra heat he needs, the 15 may honestly not be enough. For the uth once you get a heat bulb you probably won’t need it, or you could use it for nighttime heat. When there on the side unless your room sits somewhere around 75f they really don’t do much, a lot of times you need 2. One on the side and one on the back. I would just stick with a bulb and hook it up to a thermostat or buy a cheap lamp dimmer from wal mart and you can control his temps that way. Remember to that they need a few degrees temp drop at night and if you can’t get ahold of a thermostat a dimmer helps with the lowering of temps a lot.