Try making them a small pen, or buying one. They won't sit still for long. Chickens are foragers and they need room to graze. You will also want to pen them in to protect them from stray cats, stray dogs, and other animals.
Then get creative with your coop. We have no idea what your set up is, can you block off part of your coop and supplement heat at night? They dont' need to be outside, maybe larger boxes inside? You're going to have to brainstorm, cause you've still got a few weeks until they're usually good to go outside on their own.
Yes, I would also say, put them outside. I have not got much experience, but mine are only 5 weeks old and one of them has been flying around since it was 3 weeks or so! He can fly about 3 foot high!
I would try and get them outside while the weather is nice. I started mine by putting them out in the day and back in the brooder box. Then I left the light of for a couple of nights and now they stay outside all the time.
OH, I so want my flock outside, but looks like that run will not get done this week-end...mine will be 5 weeks tomorrow and have been in their coop for 2 weeks now, as they really needed the space. I had a 4' by 4' by 2' high brooder box, in my little cabin living room...at 3 weeks, once in their coop, it being summer and all, they were flying all over the coop...it was a blast to watch them, but now, poor things, they are trying to follow me out the door, when I go do chores in the coop, which is often...I feel so bad for them...but only one of the guys came up, this week-end, and they have the truck, so...my flock is stuck inside the coop for another week...sigh!!! I don't dare let them free range, too many predators, and with 15, even if I could figure out how to get some kind of "pen" made...I'm not sure I could catch them all to put them back in their coop...they run so fast now and can fly high enough to get in the trees also!!! and I fear, if they are outside, even in a pen...they won't want to go back in the coop...who could blame them, right? I'm just not young enough to catch them, should any escape, nor fast enough anymore
plus, we have sooo many places they could run to and hide, including blackberry bushes 4 feet deep...I live in a very rural area!
I think my fear of predators is a bit over the top, but I really don't want any more mishaps...one was enough! Not a predator attack...just a horrible accident, my fault too...in my defence, the first day after I put them in the coop, I saw a chicken hawk, circling the coop...I put out some poopy shavings out by the coop, from their brooder box, back when they were inside, just to see if something would come around, and sure enough, something big, strew all the shaving all over the place...not willing to take the chance with only having 15, and them being so small...not till their fort knox run is done!!!