What do you consider to be low? Anecdotally, the Google app on my phone almost perfectly recognised, played over speakers, this fairly rapid dialogue between two people encoded as 6 Kbit/sec Opus.

https://ryanplant.net/love.wav

Its only mistake was missing the "you" in "you want to be."

Codec2 remains fairly clear down to human ears down to 2.4 Kbit/sec but I had no luck getting it recognised, even with much simpler and clearer samples.

This individual anecdote tells you nothing about the state of the art, but I wanted to note it anyway because I was astonished at how well 6 Kbit/sec is handled.