I have an extremely hard time believing that. I could see maybe 20%...at the extreme high side being hardcore (accounting for their ‘elite/military), but no slave state in history ever had 85% of the slaves wanting to stay that way.
The closest thing to North Korea was Communist Albania, and when it came time, it was clear that FEW Albanians were fans of the Communist regime, it just was a matter of overcoming their fear to protest.