feeding them as much crix and veggies as they can eat? A lot of dragons will eat more than 25 crickets a day when they're in that high growth stage. The 15 month old beardie...it's probably just better that you don't give him access to a lot of crix because he's at that time in his life now that he should be eating way more veggies than crix (about 60-80% veggies to 40-20% meat). Otherwise they can run into kidney problems not so far down the road. If he has completely stopped growing by now you should probably feed him as much greens and veggies as he wants (make sure he's eating them), and 5-10 crix every other day. In the wild their meat intake is naturally lower than their veggie intake once they hit full size because their hunting skills aren't what they were as babies, so they have to eat veggies out of necessity. That's one theory at least. Plus a lot of them just naturally know to eat veggies, and some even like them better than crix.
Also, what are your temps like? You need basking temps over 100 degrees. A lot of people swear by higher temps. I'd say up to 120 is fine. you have to judge by how the animal takes to it. If you raise the basking temp and they never go up there, then it's probably too hot. If they are just constantly basking, it's probably too cold. Once it's just right you should notice a good ratio of basking to eating/exploring/etc. Proper temps and food are probably the most important aspects of reptile keeping, and those are the two that are most often overlooked. I made that mistake with my beardie when i first got him and now we're both paying the price.