Personally, I like having a coop and enclosed run. Then allow them outside of that area at my convenience.
Not to rain on your parade, but you really do not want to max out your numbers in the beginning. This will lead to frustration on your part. We don't know the size of your family, but that many birds are going to make about 7 dozen of eggs per week and cost more to feed.
There is a rule of thumb of 4 square feet per bird, so that house assuming that is that size, should hold about 7 birds. Those of us that have been doing chickens for a long time, know that too many chickens make for all sorts of bad behavior and highly stressed birds, which can ruin the hobby for you. That may be why they are getting rid of them down the road?
I can understand wanting to get laying hens, because it takes forever for those chicks to get big enough to lay. However, young pullets like that should sell quickly. See if you can get 3-4 of those layers, that would get you started, fit nicely in that set up, leave you a little room to work with and not cost much in feed, also leave you a nice back yard.
Personally, I think 15 is too many for your set up!