“American Idol,” the popular singing show that started the career of music stars and ushered in a slew of copycats, will end its run on Fox after its 15th season concludes in 2016. The network said Monday this upcoming season would be Idol’s last, pulling the plug on a show that turned contestants, judges and its host, Ryan Seacrest, into global celebrities. Though the audience has dwindled in recent years, the show remains one of Fox’s most-watched programs, and its end signals a programming reboot by Fox’s new leaders, Dana Walden and Gary Newman.