Chuck Schumer:

>“We have a population that is not reproducing on its own with the same level that it used to. The only way we’re going to have a great future in America is if we welcome and embrace immigrants – the Dreamers and all of them, because our ultimate goal is to help the Dreamers but [also] to get a path to citizenship for all 11 million or however many undocumented there are here,”

Chuck Schumer, who is massively understating the number of illegals here, puts it at at least 11M. So yeah tens of millions is a realistic ballpark.

That 11M represents decades of migration. It's not getting tripled with the flip of a switch.