Yep. Intuitively, sound propagates when particles bump into each other and transfer energy. Lower pressure means lower density, so there are fewer particles, which means it takes longer before an energized particle happens to bump into another one and propagate the wave.

Here's a graph I found. It appears highly non-linear.

https://sooeet.com/speed/speed-of-sound-in-atmosphere-graph....

Probably because that isn't just v vs. pressure, it probably takes the temperature into account as well.

The speed of sound is invariant to changes in pressure, it is temperature that matters.