Are my bearded dragons full grown adults?
15 1/2″ is a tad small for a full grown adult, but they still have some growth left in them. If I could see a pic I could get a better idea if they are just a little short, or if they seem undernourished. Continue to feed them once a day, as many bugs as they want in one sitting. Also provide a salad of a dark, leafy green (like collards) and some other healthy veggie (like squash) every day. They should be starting to eat more veggies than bugs by now so you may need to increase the size of their salad. In a couple months, you can move the feedings to every other day and by the time they are 2, you can get by with feeding them about 50 cricket-sized bugs a week, either a few every day, or a large amount twice a week, or anything in between. If you use bugs that are bigger than crickets, the actual number will be a little less, like 30 supers. Here is a good site to show which bugs and veggies you should feed your dragon (and which ones you shouldn’t!):