King suffered a surprise 3–2 defeat to German teenager Max Hopp in the first round of the 2015 World Championship. He lost 10–3 in the first round of the Masters to James Wade. King showed his best battling abilities at the UK Open to defeat Gary Anderson 9–8 after being 8–4 down and surviving 13 match darts from Anderson. He then overturned an 8–5 deficit against Nathan Derry to win 9–8 and emerged successfully from a deciding leg for the third game in a row by beating Kyle Anderson 9–8 to reach the quarter-finals. He met Stephen Bunting and the first 12 legs went on throw, before Bunting took four unanswered legs to inflict a 10–6 defeat on King. The rest of 2015 proved to be disappointing for King as he was eliminated at the first round stage of the World Matchplay, World Grand Prix, European Championship and Players Championship Finals and could not get out of his group at the Grand Slam.