In June 2015 at the inaugural 2015 European Games in Baku, Kozlov won the gold medal with the Russian Team in men's 4 × 100 m medley (with Daniil Pakhomov, Anton Chupkov and Filipp Shopin touching in 3:36.38), a new junior world record breaking the previous record held by Russia in 3:38.02 at the 2014 Youth Olympics. and in 4 × 100 m mixed freestyle (with Arina Openysheva, Elisei Stepanov and Mariia Kameneva at a time of 3:30.30). Kozlov also won bronze in the individual men's 100 m freestyle and with the Russian Team in men's 4 × 100 m freestyle.