Q: how to unlock error 1015

Here is what Apple says about error 1015.

Error 1015: This error is typically caused by attempts to downgrade the iPhone, iPad, or iPod touch's software. This can occur when you attempt to restore using an older .ipsw file. Downgrading to a previous version is not supported. To resolve this issue, attempt to restore with the latest iPhone, iPad, or iPod touch software available from Apple. This error can also occur when an unauthorized modification of the iOS has occurred and you are now trying to restore to an authorized, default state.

If you have indeed jailbroken your device, you will need to seek help elsewhere.

You need to use another admin user session to bypass the hosts file or edit the hosts file.

The last one: http://support.apple.com/kb/TS4451?viewlocale=en_US

Live long and prosper!