13.5 million sounds pretty little to me. Even the US alone boasts millions of Jews. Maybe that’s only the deeply religious ones.
I am only quoting an officially claimed repository of information on Jewish stats.
The number that south40 claimed, of 810 mil Jews worldwide, is wildly at variance with what I found when searching.
The suspect number is the 810 million. south40 used this number in posts to argue that the ratio of worldwide muslims to worldwide jews was not that much of an imbalance between the two populations.
If you think the 13.5 is too small or doesn’t reflect all jews, just observant ones, then you can look it up and see what you find. Just remember while you’re at it that the suspect number is the claimed 810 million from south40.