North Korea would fall much faster than Iraq. The real problem would be the apocalyptic humanitarian crisis and colossal burden of post invasion tasks which would make Iraq look like community days.
If NK were to suddenly implode through a shaky coup (but with Young Fat on display a la Ceausescu), the PLA would push 10 divisions over the border and fling their shitty Navy into SK waters.
The humanitarian crisis would be how much of the border and Seoul could be protected from rogue NK incursions ie they steal everything until caught in the headlights and then claim asylum.