You can think about it in terms of dB. 0.15% is about -56dB, so that means the distortion products they measured were 56dB below the signal. That isn't likely to be audible, especially if the distortion is in the harmonics we find "pleasing" like the 2 and 3.
You can think about it in terms of dB. 0.15% is about -56dB, so that means the distortion products they measured were 56dB below the signal. That isn't likely to be audible, especially if the distortion is in the harmonics we find "pleasing" like the 2 and 3.