You guys are kind of freaking me out as to possible battery issues in my future. Should I be concerned? What are your thoughts?
Stop updating so Tesla can't cripple your car intentionally and enjoy its magnificence. There's nothing to worry about if it's running OK and the only worry you should have is from updates that might take that away from you. If you have any real problems that cause a failure, the warranty will cover you, and updates on an old 2015 will only make your car worse so keep it the same!