You can find the recommended sizes in the manufacturer's website.
https://www.schwalbe.com/en/reifenmasse

This article says that a rim internal width of 50% to 65% of the tire width is a good estimate. And up to 38 to 70%
https://bikerumor.com/2016/08/12/tec...-best-results/

The description of your rim as being 20"x1.5/1.95 doesn't mean anything. What's important is the internal width of the rim