Tratz started her senior career in 2015. In March, she competed at the Cottbus World Challenge Cup, where she qualified for the vault final and finished fifth. In April, she competed at the 2015 European Artistic Gymnastics Championships, where she qualified for the all-around final and finished 18th. In September, she competed at the German National Championships, winning a silver medal on vault and a bronze medal on floor exercise. In October, she competed at the 2015 World Artistic Gymnastics Championships and helped Germany finish 12th in the team competition.