In June 2015, 16-year-old Pakhomov was selected to compete at the inaugural 2015 European Games in Baku, Pakhomov won four gold medals, in (200m, 100 m butterfly), in 4 × 100 m mixed medley (with Anton Chupkov, Arina Openysheva and Maria Kameneva at a time of 3:49.53) and in 4 × 100 m medley (with Anton Chupkov, Vladislav Kozlov and Filipp Shopin touching in at 3:36.38), a new junior world record breaking the previous record held by Russia in 3:38.02 at the 2014 Youth Olympics.

[1] Pakhomov also broke a new junior world record in 100m butterfly.

[2] On August 2–9, Pakhomov appeared in his first seniors at the 2015 World Championships in Kazan, competing with Russian Team in 4 × 100 m mixed medley (with Yulia Efimova, Vladimir Morozov, and Anastasia Fesikova) where they finished 5th and in men's 4 × 100 m medley (with Kirill Prigoda, Evgeny Rylov, and Vladimir Morozov) also finishing 5th in the finals.

In Team events, Pakhomov also competed in 4 × 100 m mixed medley (with Anton Chupkov, Irina Pridhoko and Arina Openysheva) were Russia threw in a new Junior World record touching in at 3:45.85 and in men's 4x100 medley (with Anton Chupkov, Vladislav Kozlov, Roman Larin, touching in 3:36.44), taking a meets record.

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