Yang dived into the water before the starter's gun, but was given another chance because the starter heard the same whistle in the crowd that Sun heard, causing him to leave the blocks early.
Canada's Ryan Cochrane took second in 14:39.63, while defending Olympic champion Ous Mellouli of Tunisia settled for bronze in 14:40.31.
Ranomi Kromowidjojo of the Netherlands won the women's 50 freestyle to complete a sweep of the sprints.
Having already won the 100 free, Kromowidjojo clocked an Olympic-record 24.05 in the one-lap race.
Aliaksandra Herasimenia of Belarus touched in 24.28 to take the silver medal and another Dutchwoman, Marleen Veldhuis, finished in 24.39 for the bronze.
Phelps was asked about a comeback in time for the 2016 Rio Games. He gave a definitive no in response, and Bowman doesn't think he'll be back, either.
"I guess if he finds after a few years he's searching for something and thinks he can find it in swimming, he could look at it," Bowman said. "I think he's ready to explore other things. He's done all he can do here."
Phelps' teammates expect to see him down the road, even if it's not in the pool.
"He's leaving, but he's still part of the family," Hansen said.
Franklin remembers being awed the first time she met Phelps four years ago. With her five medals, she's well on her way to the kind of remarkable career he had.
"Just watching Michael swim is beautiful. You can tell that he's meant to do it," she said. "He's done so much for swimming and we're all going to miss him so much."