Lewis had taken out finishes of 141 and 125 to be 1–1 against James Wade in the first round of the 2015 World Championship. He won the first leg of the third set, but then lost six legs in a row to be knocked out 3–1. His first semi-final appearance in over a year came at the Gibraltar Darts Trophy where he was beaten 6–1 by Michael van Gerwen. Lewis was now the number two Welsh player on the Order of Merit behind Mark Webster and they teamed up at the World Cup, but suffered a surprise 5–3 loss to Hong Kong in the first round. He defeated Justin Pipe 10–7 at the World Matchplay, before losing 13–2 to Michael van Gerwen in the second round. He threw the first nine-dart finish of his PDC career at the 17th Players Championship.