FX has renewed its flagship series It's Always Sunny in Philadelphia for a record-breaking 15th season, making it the longest-running live-action comedy series in history. The show previously shared that honor with The Adventures of Ozzie and Harriet, which ran for 14 seasons on ABC. It's remarkable that this series has yet to wear out its welcome, but the truth is that it constantly finds ways to reinvent itself. Stars Rob McElhenney, Glenn Howerton, Charlie Day, Kaitlin Olson and Danny DeVito share a special chemistry together, and there's no shortage of targets for the …