I actually find it a lot harder to manage 15, than 4, especially if you want to tame them down. Stick to 4 or 5 at most, plan to replace some after you lose 2, you never want to introduce a single bird to an established flock. If you get hooked you may want a bigger coop down the road, but not everyone gets hooked, stick to the present.If you are concerned that 4 chicks doesn't give you any wiggle room if something were to happen, get 12-15. Raise them to 8-10 weeks. By then, you should have a good handle on sex and personality. Keep 4 pullets and sell the extras. It's no more work to raise 15 instead of 4 and the coop is plenty big.