Dorsey was originally cut from a USA Basketball tryout camp for its Under-18 national team in 2014. The next year, before the 2015 FIBA Under-19 World Cup began, he was invited to Greece's Under-19 national team tryout camp. He turned out to be a vital addition to the team, as he went on to record 15.9 points and 5.0 rebounds per game, and also lead the team in minutes played. The Greek team went 5–2. After winning their first 5 games, they fell to the USA in a tight semifinal, and later lost in the bronze medal game to Turkey. He was voted onto the tournament's All-Tournament Team, despite his team not earning a spot on the medals podium.