Although my females only hit about 12", I've had two alpha males that were just shy of 15" total length, and I wouldn't use anything less than 150 gal tank one of them myself, and for a pair or trio, I'd want 300+ gallons.
In my 150 my first alpha male killed all others housed with him, and I had started with 11, one inch juvies.
Mine came from Don Conkel, and I had gone to his fish farm to pick them up, and the parents easily topped 15", and were in a 1000 gal vat in his green house.
I believe in nature you don't often see those large individuals, because predation from large birds, and reptiles takes its toll (and fishing for human consumption in places like lake Lachua), but in a well kept, large aquarium 15" is not uncommon.