You didn't say whether you intend to make them serially or consecutively (edit: oops, I meant concurrently). If you can't make one 15-gallon batch, or blend all three batches together after they're done (very gently, and without unduly exposing them to air) before kegging, temperature control is probably where you want to concentrate. I suggest you keep them ...
Press your spent grain
Something often overlooked in all grain brewing, but will greatly boost your mash efficiency. A lot if methods and devices have been created.
The commercial HEBS system gets most of it's effeciency from the press that leaves spent grain almost dry.
BIAB - hang mash bag over kettle and use high temp silicone gloves to squeeze out ...
Leave the hot and cold break behind. Use your whirlfloc and Irish moss properly. If you use them in boil and put all the hop trub in your fermentor you're just wasting space and limiting your final volume. Calculate your postboil volume to account for trub loss.