Cronin was named in the Ireland squad for the opening rounds of the 2015 Six Nations Championship on 1 February 2015. He came off the bench against Italy on 7 February 2015. Cronin suffered a knee injury during the game which required a minor surgical procedure. He was named in the Emerging Ireland squad for the 2015 World Rugby Tbilisi Cup on 19 May 2015. Cronin started in the 33–7 win against Uruguay on 17 June 2015. He also started in the 45–12 win against Georgia on 21 June 2015, a win which secured the tournament for Emerging Ireland.