I'd say around 15 million.

Has now moved 7m

#MHRise has now shipped over 7 million copies worldwide, and we couldn't have done it without you! Check in with Senri the Mailman to claim Kamura Pack 3. 💌

As always, thank you so much for your continued support! ❤️ pic.twitter.com/3etXEx33cN

— Monster Hunter (@monsterhunter) May 28, 2021

So, tracking the announcements so far:

3/29/2021,  4 million
4/04/2021,  5 million
4/27/2021,  6 million
5/27/2021,  7 million

They are selling about 1 million a month at this point, but obviously the rate is slowing.  I'm thinking they will hit 8 million sometime in July.  This game definitely has legs.

7.5m now

https://www.capcom.co.jp/ir/english/news/html/e211004.html

At this point it'll hit 8-9m on NS alone and might reach that mark before Sunbreak arrives, with PC Rise could potentially hit 13-14m tbh.

Will be interesting to see how Rise performs compared to World on PC, would assume Rise will sell less.

Monster Hunter World sales were actually leaked in the major Capcom hack at the end of 2020.

PS4 - 8.90m
PC - 5.95m
Xbox - 1.79m

PC sales looking great here, also PS5 almost 5:1 Xbox is brutal!
But yeah, Rise will be luck to reach 2/3 of World, something close to 10M, still amazing sales.

Is at 7.5 now on switch and looks like i will end up similar to world on PS4 if the PC version also sell similar to World PC version it should pass that 2/3 mark easily.

It might surpass World on PS4 seeing as MH World was at 8M total in 7 months where MH Rise hit 7.5M total in six months. Given the 5:1 split it means that PS4 was likely at 6.7M on PS4 during this timeframe. Since PS4 grew to 8.9M the Switch could very well cross the 10M mark.

If MH Rise sells similarly to World on PC then it could end up just one to two million behind MH World. It's honestly a LOT closer than I expected. 

Edit: It looks like I was foolish and was looking at an incorrect date. I was being too hasty. MH: World sold 8.3M by June 30th (which is about five months and four days), whereas MH: Rise sold 7.5M by October 4th (which is about six months and 8 days). Props to Kyuu for pointing this out in this thread and the article. Don't want to misinform. 

Just to correct myself completely, when I initially looked I was looking at the article date, but it was a fiscal report which is a month behind (It was IGN and I wasn't thinking about it). I gotta be more careful when I'm looking at that stuff, I'll edit my above comment. 

Assuming similar splits (which is most likely accurate), PS4 should be at 9.25M now.

MHW reaching 18.7M results in PS4 being 10M, which should happen.

Since Iceborne requires World,

PS4 had 61% of Iceborne sales, LTD is at 8.2M -> 5M on PS4/5

Total MHW sales on PS4/5 = 14.25M