In March 2015, Jaer was named in an extended South Africa Under-20 training group as part of their preparation for the 2015 World Rugby Under 20 Championship. While he didn't feature in a friendly match against a Varsity Cup Dream Team in April 2015,&lt;ref name="Varsity Cup XV 24-31 South Africa U/20"&gt;&lt;/ref&gt; he was included in the squad that toured Argentina in May 2015. He started their first match, scoring a try in a 25–22 win, but didn't feature in the second match. Upon the team's return, he was named in the final squad for the 2015 World Rugby Under 20 Championship. He played off the bench in the first of their three matches in Pool B of the competition, a 33–5 win against hosts Italy, but was not named in the matchday squad for their 40–8 win against Samoa or their 46–13 win over Australia, 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. Jaer was used as a replacement in their semi-final match against England and scored South Africa's first try of the match in the 77th minute, but could not prevent them losing 20–28 to be eliminated from the competition by England for the second year in succession. He started his first match of the competition in their third-place play-off match against France, helping South Africa to a 31–18 win to secure third place in the competition.