"The Earth could sustain 16 Billion humans or more..."
Sheerest nonsense. Not at any standard of living that people would find tolerable. Your country exists with its high density due to external resources that are inported. Furthermore, most of the planet is uninhabitable or nearly so -- Mountains, Deserts, Rain Forest.
The planet can sustain, for the long term, probably no more than 2 billion, likely far less.