If you upgraded to to WP10 Insider Preview for the 1520

After a few weeks trying out windows 10 on my 1520 I'm happily back on 8.1. Forgot how much I liked it. No bugs and everything runs smoothly. Windows 10 just wasn't ready enough yet for a daily driver. It seemed like it was getting worse and not better. My first week with it was great, second week OK, third week I was having random restarts all the time and a few screen freezes. Some apps that worked at first stopped working.... Back on 8.1 for now. Will wait patiently now for the final build to upgrade. Good news is that there really wasn't anything super compelling about windows 10 mobile that I feel like I'm missing right now.

That was my experience, too. I needed a phone which wouldn't freeze, or require a reboot to drop a call, or wake up the phone. My L1520 is back on 8.1. But honestly I am going to give the upcoming preview a chance, as using the recovery tool to go back was not painful last time.
 
As a Lumia 1520 owner currently downloading 10536, I think many people confuse "Apps" with "OS" and attribute issues with Windows 10 to apps that have not been updated yet.
 
You may be right Erik. Either way it was (is) buggy as hell. Not ready for a daily driver. It mostly worked except when it didn't which was getting more and more frequent for me somehow. I actually have more features and better stability back on 8.1 so besides the curiosity of what new there is no real reason to be on 10 right now.