[4] Coleman made his first appearance for the senior team aged 18 on 31 August 2015 as he came on as a substitute for Kevin O'Connor in a 3–1 win over St Patrick's Athletic at Turners Cross.
[6] He captained the under 19 side to the Enda McGuill Cup, beating St Patrick's Athletic in the final and qualifying for the UEFA Youth League in the process.
[7][8] Coleman impressed in the UEFA Youth League, as he captained the side to a 1–0 win on aggregate against HJK Helsinki of Finland before losing 3–1 at home and 1–0 away to Italian giants AS Roma.
He amassed 35 appearances and 2 goals across all competitions in his first season at Premier Division level which included playing both legs of the Promotion/relegation playoffs, which saw Limerick beaten by Finn Harps, resulting in relegation for the blues.
[18] This performance helped Coleman claim his place in Harry Kenny's starting 11 over the next number of games, just before Pats' UEFA Europa League campaign.
[19] Coleman got his first taste of European football at senior level as he played both legs of the tie as Pats were knocked out of the UEFA Europa League at the first hurdle by IFK Norrköping of Sweden, losing 2–0 at home[20] and 2–1 away.