I am new to raising chickens
Hi! I'm new to this site as well. I have had chickens for 6+ years, so I have experienced some things. The broody hens are not laying the eggs. The other hens in your flock will share the same boxes, adding to the gene pool. 15 is probably a good number. I'm not nearly as experienced as others on here, but I would use a marker to mark the eggs that are there, and remove all the others that arrive. OR section off the coop to separate the flock, which is DEFINITELY what you'll want to do once the chicks start hatching...other chickens can be very aggressive.
Again I admit that I am a relative novice on this site, but I saw that no one had replied to you, and I wanted to try to help.
I went out and one of my broody hens was not laying on her eggs but on the ground under them and I found one of the eggs with a hole in it and a chick moving around in it. My boyfriend removed the rest of the egg and we brought it inside into a box with a warmer under it. Keeping it at 99 degrees. I hope it makes it. But she has 16 eggs under her. We don't know how many the other one has. It will be interesting to see what we get.