This is an interesting forum. In particular I think it I important to differentiate coop and run. If there's 15 chickens in a run that is 150 sq ft plus a coop to fit them for laying and overnight, the chicken math pans out OK. Sure it may be a bit busy, but there's sufficient space (not to mention far more space than the big chickens companies provide). The run needs to provide open air, often an area enclosed with hardware cloth or chicken wire attached to wooden posts/framing will suffice. The coop is not the open air section, but an enclosed, yet well ventilated structure. It's rare that somebody with 30 chickens would have a 150 sq ft coop. If it is like the picture chosen by BYC on the home page, that's a covered run.
The reason I make a point to differentiate the run and coop is that it would be hard on the chickens to keep them in a fully enclosed coop (building) of 150 sq ft because conditions would get poor very quickly - air quality, dust, etc. However, providing a 150 sq ft open air run is much different. It allows for fresh air to constantly come in and for poor quality air to escape. Dust is kept down by moisture from the air and precipitation if you are not covering the run. There's advantages to covered run though, in particular it keeps a lot of snow and rain out. Just don't cover the sides, only the roof. The coop is where chickens can go to escape the elements and gain protection.
The reason I make a point to differentiate the run and coop is that it would be hard on the chickens to keep them in a fully enclosed coop (building) of 150 sq ft because conditions would get poor very quickly - air quality, dust, etc. However, providing a 150 sq ft open air run is much different. It allows for fresh air to constantly come in and for poor quality air to escape. Dust is kept down by moisture from the air and precipitation if you are not covering the run. There's advantages to covered run though, in particular it keeps a lot of snow and rain out. Just don't cover the sides, only the roof. The coop is where chickens can go to escape the elements and gain protection.