Car failed at the 15mph with high NO levels and passed fine at 25mph with low NO levels.

Could this be a potential lean out at low rpm? my car has a tune, so is it possible i need to make it more rich?

I guess NO gas is from a hot engine core.. any way i have no clue someone help if possible.

 

I would say your assumption is right on the money.
How where your hydro carbon levels if the were low I would say for sure.

 

Give us the rest of the numbers. But yeah, NOx is created when combustion temps reach 2500 F = lean or an ignition timing issue