You could consider buying it online and having it shipped. Check
walmart, chewy,
tractor supply, etc. Sometimes the shipping is too expensive to be worth it, but sometimes they will offer free shipping on certain size orders.
Check what other feeds are available at your store.
Layer pellets have enough calcium for laying hens (more than other chickens would need.) But if you provide a separate source of calcium, like a dish of oyster shell, you can feed them any complete chicken food and they will do just fine. So look at the price for chick starter, grower, all-flock, flock-raiser, and whatever else they have. Sometimes another feed is so much cheaper that you can buy oyster shell separately and save money, and sometimes Layer Feed really is the cheapest choice. You do need a complete feed with a reasonable protein content, so don't try to use plain corn or scratch grains.
Check whether the chickens are wasting the food, and whether anything else may be eating it (like rats or mice.) You do not want the chickens to go hungry, but there is no point in paying for feed that they do not eat.
Adult laying hens will often eat about 1/4 pound per hen per day, so I might expect 15 hens to eat over 100 pounds of feed in a month. You don't say what size bag of feed you are buying, or whether you are feeding other things too, but do make sure they are getting enough to eat. The amount per hen varies somewhat, depending on the size of the hens and how many eggs they are laying, but it is still a handy check for whether the feed usage is in the right ballpark.
Of course you can also save money on feed by having fewer chickens. (Not a fun choice, but something to consider if the feed cost becomes a real problem.)
