My chickens waste a ton of feed by flinging it onto the floor. I nearly eliminated this by raising the feeder to just enough for them to crane their necks around and eat. If the floor still gets too much feed on it, I take their feed away for a day. Surprise! They find the food on the floor and eat it ALL!
It does sound like you're going through too much, as I'm guessing a bag should last you about 20 days, not 14. Definitely check for rodent problems, and make sure there's not a bunch on the floor.
How big is your yard? Is it possible to build two runs and let them eat down one, and then switch to another?
You can also build a cheap grass saver, by making a 2x4 frame with chicken wire over the top. That way, they can't wreck the root of the grass, therefore letting it grow more for them to eat. Plus, the outcome of their dinner will fertilize the grass!

It does sound like you're going through too much, as I'm guessing a bag should last you about 20 days, not 14. Definitely check for rodent problems, and make sure there's not a bunch on the floor.
How big is your yard? Is it possible to build two runs and let them eat down one, and then switch to another?
You can also build a cheap grass saver, by making a 2x4 frame with chicken wire over the top. That way, they can't wreck the root of the grass, therefore letting it grow more for them to eat. Plus, the outcome of their dinner will fertilize the grass!