A number of program/security flaws and patch fixes are common for new releases to both Apple and Windows OS. BTW, Apple long ago dropped their claim that their OS is resistant to malware, and suggests using additional security apps for increased protection. Though both Windows and Apple OS come with basic malware protection included.
I generally stay away from OS upgrades during their initial release, both Apple and Windows, as flaws tend to show up with a wide release not apparent in beta. iOS 9 is no exception.