After waiting a few months, I decided to compare the release dates in previous Stormlight Spanish audio books on Audible:
Way of Kings
English - Aug 31, 2010
Spanish - Nov 19, 2020
Delay - 10y, 3mo
Words of Radiance
English - Mar 4, 2014
Spanish - June 24, 2021
Delay - 7y, 4mo
Oathbringer
English - Nov 14, 2017
Spanish - Nov 25, 2021
Delay - 4y
Rhythm of War
English - Nov 17, 2020
Spanish - ?????
So, the delay has been decreasing over time, but the most recent delay was about 4 years, so a very rough guess at approximate Spanish audiobook release date would be sometime in late 2024 to early 2025.