Take your mattresses, pillows and blankets out to have some fresh air. Spank them and keep them out for a day - so long, dust mites!
Defrost your freezer. Take the frozen food out into balcony, plug off the freezer and let it thaw. Have a bowl and a cloth close by, you will need to wipe and collect the melt-water. Patience, you don't want to remove the ice by stabbing - violence breaks the freezer. After you've gotten rid of the ice, plug in the freezer, let it cool and restore the food. The whole process takes few hours.
Dust the carpets by beating them on snow. Rock away the excess snow and take the rags back in. Like dry cleaning, but free of charge.
Why below -15 C? Because the dust mites are able to survive up to -18 C. Because the frozen food is used to spend time around -15 C temperature. And because -15 C snow is fine enough and doesn't water the carpets.