From last weeks Oculus VR Jam Q & A:
“–]Gypsy816Community Manager, Oculus VR[S] 4 points 4 days ago
Hi there! We’ve provided KitKat for the judges to use so if you’re already using KitKat, continue to use KitKat.”
I reverted my Note 4 to use KitKat and the performance is much better (though still not ideal…)