Q: my iphone 3G won't restore because of error 1015

Hello, nanipan. 

Thank you for visiting Apple Support Communities. 

Here is an article that you may find helpful with this issue. 

Check for hardware issues

Try to restore your iOS device two more times while connected with a cable, computer, and network you know are good. Also, confirm your security software and settings are allowing communication between your device and update servers. If you still see the alert when you update or restore, contact Apple support.

Common errors: 1, 10-47, 1002, 1011, 1012, 1014, 1000-1020.

Resolve specific iTunes update and restore errors

http://support.apple.com/kb/ts3694

Cheers,

Jason H.