3,000 dead of 80,000 or so infected. There's the higher bound 4% death rate.
You seem to suppose that the rest of China's population won't get it. That quarantine is effective. That would be a really optimistic assumption. Rosy to the power four.
Obviously, not many people are making that assumption, but they do see that the rate of distribution in China seems to have slowed some. And that is probably one of the reasons why 15m instead of 60m.
Italy has just adopted the Chinese model. So people must think it works to some extent.
But nearly everyone assumes that only slows down the spread. It doesn't stop it altogether.
So, total population, times the infection rate, times the death rate, times the rosy fraction, if you prefer.