It's odd that you have not caught any bluegill as of yet.

The Green Sunfish could also have come from the wet-weather-creek, but there's also a chance that they were mixed in with the bluegill stocking.

A 15" LMB can eat many 3-5" bluegill, so the larger the bluegill that you can get, the better chance of survival. If you can't source any larger bluegill, then maybe add 25-30% more in the actual number of bluegill to stock to factor in predation.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."