Plug two system/airflow fans into the sys_fan header (with a splitter) and the cooler fan into the cpu_header. Or get a fan controller for all non-cooler fans. The sys-Fan header will probably be 3 pin voltage controlled and the cpu_fan will be 4 pin PWM controlled. Plugging one into the other means the fan runs at full speed.
Actually, says this in the spec https://www.asus.com/Motherboards/B150M-A-M-2/specifications/
1 x CPU Fan connector(s) (1 x 4 -pin)
2 x Chassis Fan connector(s) (2 x 4 -pin)