St. Fort's first international competition came at the 2015 World Youth Championships in Athletics, where the 100 m was seen as a duel between her and America's Candace Hill (who had recently broken the World youth best). St. Fort produced three personal bests at the competition, running 11.39, 11.24, then 11.19 seconds in the final to secure the silver medal behind Hill. A 100 m gold followed at the 2015 Pan American Junior Athletics Championships in the absence of Hill. Her last major outing of the year was a senior debut at the 2015 World Championships in Athletics. She was chosen as the relay alternate and competed in the heats of the 4×100 metres relay, where she broke the Trinidad and Tobago national record with a time of 42.24 seconds, anchoring a team of Kelly-Ann Baptiste, Michelle-Lee Ahye and Reyare Thomas. In the final, she was replaced by Semoy Hackett and the team improved the record further in their bronze medal-winning run. The 17-year-old St. Fort received a bronze medal as the heats runner.