Pokemon really is something. There really are few franchise that have been around as long as it, and even less that seem to endure with such impressive sales. If you were expecting that to change with Sun and Moon, it looks like you are mistaken.
It's being reported by Gematsu that in Japan alone, the game sold 1.9 million copies in the first three days. What's really something, is that number doesn't even include digital sales. That is better than some AAA games sell world wide!
Once we include the numbers of the US and places the game isn't out yet, like the UK, this could be one of the fastest selling games this year. Not bad going for a 20 year old franchise.