Cameras on an iPhone are in general better than those on Android devices, at least that's my experience. The 6s plus has a 12 MP rear camera, and a 5 MP front camera, and it takes excellent pictures.
3D Touch would be another reason to switch to the iPhone, imo. This feature helps fulfilling tasks more quickly than on other phones.
If you intend to use the software as Apple provides it, there's no need to buy antivirus apps. In fact, there are none in the App Store. Apple's way of keeping apps "separated" (sandboxing) makes it impossible to get malware or viruses to the iPhone.
If you want to jailbreak your iPhone, that's also possible. Not yet with the latest software (9.1), though.
There are regular software updates with additional security content and improvements, and they are released to all the iPhones around the world at the same time. There's no delay.