At 10 deg Celsius with the fan on the 3rd step (strongest) I still need a towel to wipe away the sweat at every 2-5 minutes. At 15 deg Celsius and the same fan at the maximum speed, I can't avoid a puddle of sweat falling on the floor, no matter wiping with the towel.
How could one possibly ride indoor without a fan? Maybe try sauna bath instead?