Oh absolutely.It doesn't specify the size of the coop it's self, but comparing it to the run and the size they give for that, I don't think it's anywhere near large enough for 18 chickens. I know they say 15, but prefab coops are notorious for dramatically over estimating the number of birds they can effectively house.
Mine supposedly can house 15-18 and I would never put that many in there.
More like 8 and only if they free range also.