The network said next season will be the 15th and final for the talent show, which at its peak was the most dominant program on television and ushered in a new era of competition shows that changed the TV landscape. But the audience for the program, hosted by Ryan Seacrest, has been waning in recent years and high-profile sponsors started to lose interest. The decision to cancel “American Idol” is part of a slew of programming changes in the works at the network, which is coming off one of its most disappointing seasons ever. The network is in fourth place in both total viewers and the coveted 18-49 age demographic. Fox said it will launch nine new shows in the 2015-16 television season as it bets on big names.