There are ways to downgrade your OS to KitKat (4.4). There are a lot of third party sites that are really good at keeping up on all the files and drivers you need to do it.
If you're not tech savvy, I wouldn't suggest doing it. It's easy to mess up, and if you do that you'll be dealing with a slew of other problems. And it sounds like you can't afford any downtime on your phone anyway since you're trying to run a business. I can certainly appreciate that.
If you're confident and want to try it, check this out as a starting point: