It was a typo, but not a big one. Meant to put 15k (15,000). Which are correct numbers. ROPD is accurate and usually up-to-date, but of course, it counts every character, regardless of whether or not they're on one account. So, it's probably a little below 15k, but probably not much. Then there are also those who use multiple account, but still, it's in the range of 10k-15k. Valkyrie has been popular for awhile, and has had a huge player base, which is why some people I know have avoided playing it.
Chaos has peaked 10k before, and the official servers (Chaos, Iris and Loki), were probably well over 20 all together.