Note: This process is the same for all devices. Therefore we will refer to the old iPad as old iPad and new iPad Air 2 and iPad Mini 3 as just iPad or New iPad.
iCloud can be one of the most helpful things you have on your iOS device. If you have never used iCloud you will need to go through the initial set up process.
Launch Setting > iCloud > Storage and Backup tap on Back up Now button. This could take a few minutes depending on what size your iOS device is and how much data you have which needs to be backed up.
After the Backup completes check to make sure it shows the current time. This ensures your backup was completed successfully.
Turn off your old iPad Note: It can cause conflict during the backup and restore process at this time.
Follow the on screen instructions of the New iPad to complete the setup. It will have you choose language, Country, enable Location services, Wifi. Just like you did when setting up the new iPad.
Tap on Restore iPad from iCloud Backup
Enter your Apple ID and password, tap next
If you have chose two step verification you will have to complete the verification code sent to one of your trusted devices. Tap on Send
Enter the four digit verification code sent to your trusted device
Agree with terms and conditions
You will now see a list of the backups you have made in the past. Choose the latest backup of your device and tap restore. This can take a bit of time depending on the amount of data in the backup. So you should be able to make a guess at the size of the content you backed up.
The device should now restart and restore is complete. We do recommend you now connect your device to iTunes so you can transfer any content which may not have been in the backup such as music, apps, video, sand so on.
The iPad will now begin downloading all the items in background.
Once the iPad finishes you will now be able to use your iPad with the data from your old iPad backup.