Could an alligator grow to croc sizes if...?

the record is about 15 feet i think but that is rare, american alligators were nearly hunted to extinction at one point and that of course took a toll on the gene pool especially the big gator genes, the rumors about big gators in the sewers are mostly just myths they need sunlight an alligator could very well survive a few years in a place like that but thrive? probobly not