On 1–3 May, Mamun competed at the 2015 European Championships where she together with Yana Kudryavtseva and Aleksandra Soldatova won team gold for Russia. She qualified to 3 event finals, winning gold in hoop, silver in ball and 5th in ribbon. On 15–16 May, Mamun won the all-around silver at the 2015 Holon Grand Prix, she qualified 3 event finals, winning silver in hoop and bronze (clubs, ribbon). Mamun swept her first gold for the season at the 2015 Tashkent World Cup, where she won the all-around title with a total of 75.500 points and all 4 event finals.