Having hearing sensitivity over 16 kHz is unusual. If you're under 15 years old and kept your ears pristine by not listening to loud noises, you might be able to hear it. Older people are out of luck.
Moreover, even if you can hear above 16 kHz in loud pure tones, there is so little content in real audio/music above 16 kHz that it makes no practical difference.
> massive savings ... effectively saved 25%
Not really. Going from a 48 kHz sampling rate to 32 kHz is indeed 2/3× the size for uncompressed PCM audio. But for lossily compressed audio? Not remotely the same. Even in old codecs like MP3, high frequency bands have heavy quantizers applied and use far fewer bits per hertz than low frequency bands. Analogously, look at how JPEG and MPEG have huge quantizers for high spatial frequencies (i.e. small details) and small quantizers for broad, large visual features.