To be clear, "small quantities" are in units of parts per million. 5ppm (0.0005%) and the room smells of ammonia, 25ppm means you should be wearing a respirator, 500 ppm (0.05%) can be lethal.
Warning that 15% air-ammonia mixtures can burn is like warning that 100 kg of TNT could give you a concussion if it fell on your head. It's just not the concern at all.
That seems to be true for ammonia as well, at least according to the Wikipedia page's [1] section on Combustion:
Ammonia does not burn readily or sustain combustion, except under narrow fuel-to-air mixtures of 15–28% ammonia by volume in air.
That doesn't sound too horrible, it feels like gasoline/petrol is easier to combust (although I know it's the fumes that are actually flammable).
[1]: https://en.wikipedia.org/wiki/Ammonia#Combustion