No wonder Vietnam is so behind.
Our population is indeed 15 times more, yet one Chinese makes 3 times more money than 1 Vietnamese, so our total GDP is 45 times bigger. Hong Kong, a single city, has a larger GDP than all of Vietnam.
China does consume more food, but we also consumer more per capita. Your people are starving yet still exporting food! Now that's sad.
Your population is manageable? Ok, let me make the analogy. Singapore has a small population right, but why is it so overpopulated? Because what matters isn't total population its population density. China has a low population density. Vietnam has a very high population density. Vietnam would long have exhausted its limited resources in its own borders before it is rich enough to import from the outside.
I call this phenomena "getting starved before getting rich".
China has 90% energy independence and 99% food independence. We can afford to pay farmers to leave their land untilled to reduce environmental impact. Can Vietnam? No, Vietnam has to export food even as Vietnamese get stunted due to malnutrition.