I've talked about error 1015 here in the past, so I won't repeat the whole discussion now, I just want to present you a new program called RecovBoot with which you can get the phone out of Recovery Mode after you've done a firmware downgrade, regardless of which phone you did this.
RecovBoot is better than iRecovery or RecBoot because it allows you to enter/exit the phone from Recovery Mode with a simple button press, but without the need to install LibUSB beforehand. Basically, download this program and press the top button to put the phone in Recovery Mode or the bottom button to remove it.
RecovBoot can be downloaded from here.
