That sounds rather odd for the OS itself to be the cause. Try running it in "Safe Mode" for a while and see if that changes. Yes, you will have limited access to things in "Safe Mode", however if it has a charge that lasts longer while in that mode, then you know it isn't the OS that is the issue, but something else that is on the device. Which you would need to remove to resolve the issue.
If it still does it in "Safe Mode", then while it could be the OS change, it could also just be the battery is in need of replacing. First try reverting back to the prior OS version. Just be sure you back up your personal stuff off the device before doing so. Then see if it still drains fast. If it does, it is the battery.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.