DC motor speed is proportional to voltage. The current is proportional to output torque. Output torque is the same as that of the load.

On a blower assuming squirrel cage type power is proportional to the cube of speed change.
So
if I cut the voltage by half
I cut speed by half THEN
I cut power by 1/8
and current is way way down (probably a little higher than 1/8).

12V motor on six volt should run a lot longer -- most likely will fail due to bearings which is generally the case.

Yes you can test run it on a six volt dry cell. I use 9V to see if a motor will run - not for long battery gets HOT.
Dan Bentler