[3] On 13 August, he scored a goal in the Bulgarian Supercup final, but despite his performance Botev lost 1–3 to Ludogorets Razgrad.

[4] Milen scored the opening goal in the derby game against Beroe Stara Zagora on 24 October.

On 15 March 2015, Gamakov scored the first goal with a header in a 2–0 home win over CSKA Sofia.

[6] On 16 and 23 May Milen Gamakov was included in the starting lineup as a defensive midfielder for the 3-2 home win over CSKA Sofia and the 1–2 away defeat to Beroe Stara Zagora.

[7][8] Milen Gamakov was named the second-place winner of the best youth player in A Grupa for the 2014–15 season.

In February 2016, due to a lot of injuries of his team mates, Nikolay Kostov started using Gamakov as a central defender.

Antoni Zdravkov was appointed manager of the under-21 team in October 2014 and selected Gamakov as the new captain.