If it's really tight when you spin it by hand, (holding the axle in your hand for example) then sure loosen up the cone. That's just common sense, but counting spins until it stops isn't a test for friction.

Spinning the wheel without weight on the axle does not translate into spinning while loaded. The test doesn't tell you anything. It would be better to find a slight down-slope, coast from a stop and see how far you go.