According to Ian Morris (p. 107 onwards), the largest city in East Asia in 1,500 BCE was Zengzhou with a population of 35,000. The largest city in the west was Thebes with 100,000.

The paper I linked has a very interesting side-by-side comparison of city sizes in the east and the west for the last ten thousand years, by the way. Among other things it shows that Mesopotamia and Egypt has had the edge for most of history, with Rome overtaking it at his height followed by China in the Middle Ages.