My first post of many, I am sure.....question for you experts. I have 50 RIR 3 month old chickens and they have been under a heat lamp in a "small" grow out pen (outside). I am wanting to move them to their large coop, however, my Grandma says they still need to be in a fully enclosed coop with heat lamps for the next month?? The temp only gets down to 15 or so on the extreme coldest nights. THey should be just fine outside, right?