I suggest you do a bit more research on that. Houston does not come near the ranks of L.A. ports (about 12 million container capacity) or N.Y. (about 5 million capacity). Houston (less than 2 million) is closer to that of Savannah or Charleston or Oakland, but smaller.
They do want to expand to take advantage of the Panama Canal expansion so Walmart can import even more cheaply. But that is some years away.
Oops - typo. That was supposed to be 15 million.