Well, if you don't want to turn on the heat, here are a couple of things you can do.
1. Create a separate compartment for the mushrooms that heats on its own. This might be too expensive if you only grow mushrooms this one time, but in the long run it is cheaper than heating your room to 23 degrees constantly.
2. If it's spawning right now, wait until they are somewhat big and they start spreading spores. Then pick them and put the kit in the fridge until it gets warmer. This might be a bet against contamination, but it might work.
3. Put them on the warmest place in your house (not directly over a heater, though) and pray for them. :wink: