Four days later, having amassed 43 goals for different teams over the season, Mayoral was an unused substitute in the main team's 3–0 La Liga home win over UD Almería. On 4 May, he scored twice in a 3–1 win over Celta de Vigo in the quarter-finals of the División de Honor Juvenil, and thirteen days later he concluded his reserve season by scoring the only goal in Castilla's win over CD Toledo. He was sent off on 27 June at the end of the 2–1 loss to Rayo Vallecano in the final of the 2015 Copa del Rey Juvenil at the Estadio Alfonso Murube in Ceuta, for attacking an opponent.
