Before starting his freshman season at Purdue, on June 18, 2015, Swanigan was announced as a member of the 12-man 2015 USA Basketball Men's U19 World Championship Team for the 2015 FIBA Under-19 World Championship that won a gold medal in Heraklion, Crete. On making the team, Swanigan said, "I always set goals for myself. I set goals for this spring. One of my goals is to make this team to end my high school career." To prepare for the games, Swanigan played in the Nike Hoop Summit, the McDonald's All American Game, and the Jordan Brand Classic. Swanigan did not take part in the Indiana-Kentucky All Star Game so he could attend the U19 training camp. He was one of five players returning from the gold medal-winning U17 squad. Swanigan's teammate Vince Edwards was also in the running to make the team, but was cut at the round of 16. The team finished 7–0, and Swanigan averaged 6.1 points and 4.4 rebounds per game.