Android

2 days ago, I updated my S6 to Marshmallow from lollipop. I have had nothing but problems with my phone since. My battery life is depleting 30% every hour, even when not in use ( I make sure to clear my apps, everytime, turned down the brightness on my screen..etc.) also my fast charger, the one that came in the box, is now not "fast" charging. Took my phone 5 hours to fully charge, when before it only took 1 hour.
I have an appointment with my carrier, and Im in the process of backing up everything, just in case.
Is there anyway to restore Lollipop without wiping my phone? I really want to avoid going to the carrier tomorrow. Im so fed up with this "update". Any help is much appreciated.