slow icloud backup after factory reset

I recently had to restore my iPad2 after a ios 9 update was unsuccessful / corrupted. Since doing so, I have attempted to back up the iPad2 to iCloud and the dialogue indicates that it is 'calculating time', and / or after some time it shows a 13 hour time for the backup. I use fast ADSL2 and previous backups have only taken about 20 minutes maximum. Any ideas to resolve this issue would be appreciated .