A bit late but [1] shows equal comprehension between justified and ragged-right but much faster reading speeds with ragged right (post-stroke patients in Russian). [2] shows slightly faster reading speed with justified text but less comprehension on a delayed test (also in Russian). [3] has no empirical data but cites articles and claims comprehension is equal between the two formats but ". Poor readers, however, read unjustified text more quickly than justified text."

I would say it's not overwhelming, but I'd go with ragged-right to be safe.

[1]: tug.org/TUGboat/tb38-2/tb119veytsman-justify.pdf [2]: https://tug.org/TUGboat/tb37-2/tb116akhmadeeva.pdf [3]: https://benjamins.com/catalog/idj.8.2.03sti