6 week old chicks need to go outside, but it is 15 degrees out. Any suggestions?

Hello - I have ten 6 week old chicks living in my house in a brooder. They are starting to fly out of their brooder fairly often, and are getting to be a little too much to have inside. In this never ending winter, we have been experiencing temperatures falling to less than 10 degrees (last night it was 0 degrees), with the next week looking like mid-teens each night. They seem to be fully feathered (although this is my first batch so I am not 100% sure). With the temperatures being what they are, does anyone have any suggestions? Can I put them in the coop now? Should I leave them in their brooder longer until it warms up? Should I somehow heat their coop for a week or two?

Any guidance or experience would be greatly appreciated. I am just not sure how cold is too cold for these guys… Thanks!