This is from a RAM service bulletin regarding 15w-40 in a 2019+ 6.7 Cummins
CAUTION! 15W-40 grade oil CAN NOT be used in any 2019 model year or newer 6.7L equipped vehicles due to the new designed valve train of this engine. If this oil is used, it will cause deposits to form in the Hydraulic Valve Lash Adjusters leading to undesirable noise, and/or engine damage. For any additional information regarding oil usage on these vehicles, please be sure to refer to the owner’s manual. POLICY: Information Only