Johnson suffered a hamstring injury on August 1, the first day of the Browns' training camp. He sat out the next 10 days, and the team said he would not play in the first preseason game against the Washington Redskins at FirstEnergy Stadium on August 13. During Johnson's first pre-season appearance, he was diagnosed with a concussion and was removed from the game. On September 13, Johnson made his NFL debut, running for 22 yards on 7 carries against the New York Jets. On October 4, Johnson caught 9 passes for a career-high 85 yards and his first touchdown of his career. Johnson caught a 34-yard touchdown. On October 25, Johnson caught 7 passes for 73 yards against the St. Louis Rams. On November 1, Johnson recorded a 52-yards reception against the Arizona Cardinals. On November 5, Johnson scored his second touchdown of his career against the Cincinnati Bengals, a 12-yard reception. On December 13, Johnson ran for 78 yards on 13 carries against the San Francisco 49ers. On December 20, Johnson ran for a 39-yard gain against the Seattle Seahawks. Johnson caught a pass for 22 yards. Johnson finished the 2015 season with 379 rushing yards on 104 carries and 534 receiving yards on 61 receptions and two touchdowns. Johnson's 61 receptions are the 2nd-most by a Browns rookie, tied with wide receiver Greg Little. Among rookies, Johnson was ranked 12th in rushing yards and was one of twelve running backs to break 300 receiving yards. Among rookies, Johnson ranked 1st in receptions and receiving yards among rookie running backs and 2nd in receptions overall, just under Oakland Raiders' Amari Cooper. Johnson was ranked 6th overall among rookies in receiving yards and was 1 of 6 rookies to break 500 yards receiving.