I think it's a good time, when you take into account some things, such as research, writing, editing and, of course, any thought that may arise
I think I write about 70 to 80 words per minute or so. So calculate a little slower as you write an article that you have to think about, about 50 words per minute. The actual writing time is approximately 10 minutes.
But in general, if there is research, that takes a few minutes anyway, then it is edited, tested and so on. As you say, if it's a topic that you're well versed in, it takes less time. But still, I calculate 30 minutes for each 500-word article. Just to be sure.
That way, if you get $ 15 for each, you earn $ 30 per hour. If it is a bit slower for some reason, it will never fall below $ 15.
I think many people are surprised with the time it takes to write 500 words. That does not sound like many words. however, 500 words have approximately 1.5 pages of Word. And you have to think about it, before writing and during.