In February 2015 he scored a career-high 45 points against Pacific. Wiltjer led Gonzaga to its second ever Elite Eight appearance and a school record 35-3 record. He was named a Consensus Second-Team All-American, as well as First-Team All-WCC and WCC Newcomer of the Year. In his first season with Gonzaga he appeared in 38 games averaging 16.8 points per game, 6.2 rebounds per game and 1.9 assists per game in 27.6 minutes per game. After contemplating forgoing his remaining eligibility to enter the 2015 NBA draft, Wiltjer decided to return to Gonzaga for his senior year.