On June 25, 2015, Lyles was selected with the 12th overall pick in the 2015 NBA draft by the Utah Jazz. He signed his rookie scale contract with the Jazz on July 7. Lyles averaged 3.0 points and 3.6 rebounds per game over the first two months of his rookie season. He began picking up his production with more steady minutes during the month of January, scoring in double figures for the first time on January 4 with 13 points against the Houston Rockets. On January 9, in a win over the Miami Heat, he recorded 10 rebounds for the first time, and on January 14, he scored a then season-high 19 points in a loss to the Sacramento Kings. On February 3, he was named a Rising Stars Challenge participant at the 2016 NBA All-Star Weekend, replacing the injured Nikola Mirotić on the World Team roster. On April 10, he scored a career-high 22 points in a 100–84 win over the Denver Nuggets.