I had same problem, for two days i was trying to update my phone. The problems is NSU has bug. I could not wait till Nokia team will fix it, so i kept trying.
When Service Layer Host Stopped Responding window displayed, its usually happens on 15 min on update, just close NSU with Task manager, BUT DONT DISCONNECT PHONE. After closing NSU, start NSU again while phone connected to PC.
NSU will start updating from same point where it stopped.
It worked for me.
Please note you doing it on your owe risk.
Another solution just wait till new version of NSU will be available.