Yomif opened his 2015 season at the African Junior Championships in Addis Ababa, winning the 5000 metres in 14:31.03. He made his IAAF Diamond League debut in Doha, placing fifth in the 3000 m; he then won a non-Diamond Race 5000 m race at the Prefontaine Classic in Eugene, improving his personal best to 13:10.54 and outkicking Edwin Soi and Galen Rupp. Yomif scored his first Diamond League victory the following week at the Golden Gala in Rome, winning in a world-leading 12:58.39 and breaking 13 minutes for the first time. On 11 September 2015 Kejelcha competed in the Diamond League event in Brussels and set a new personal best (and world-leading time for 2015) of 12:53.98 in the 5,000-meter event.