In January 2015, Petersen played in Q School and earned a two-year tour card on the second day by defeating Chris Hartrey 5–1 in the final round. Petersen did not base himself in Britain for 2015 and estimated he would make 20 trips back and forth from South Africa during the year. He entered the UK Open in the second round stage and beat Mark Cox 5–4, Mark Barilli 9–8, Jamie Caven 9–6 and Eddie Dootson 9–3 to reach the quarter-finals of a major PDC event for the first time. Petersen led world number one Michael van Gerwen 3–2 at the first break but had had darts to win every leg and went on to lose 10–5. He became the first South African to throw a nine-dart finish on the PDC tour at the sixth Players Championship and went on to reach the quarter-finals where Van Gerwen whitewashed him 6–0. At the World Cup, Petersen and Filby survived a match dart from Finland to win 5–4 before losing both of their singles matches against Van Gerwen and Raymond van Barneveld of the Netherlands in the second round. Petersen was invited to participate in the first World Series of Darts Finals, where he was eliminated 6–3 by Robert Thornton in the first round.