Upon the team's return, he was named in the final squad for the 2015 World Rugby Under 20 Championship. He didn't play in the first of their three matches in Pool B of the competition, a 33–5 win against hosts Italy, but came on as a replacement in their 40–8 win against Samoa in the second match. He started their final group match against Australia, scoring a try in the second minute of the match to help South Africa to a 46–13 win which saw South Africa finish top of Pool B to qualify for the semi-finals with the best record pool stage of all the teams in the competition. Vermeulen didn't feature in their semi-final match against England, which saw them lose 20–28 to be eliminated from the competition by England for the second year in succession but he did start their third-place play-off match against France, helping South Africa to a 31–18 win to secure third place in the competition.