Just got a new iPhone 13 and that new iPhone smell is still on it? Well, it might be new but that doesn't mean that you don't need to update it.
Yes, it's running iOS 15, but not the latest iOS 15.
Yes, the update treadmill starts on day one.
According to Apple, "[t]his update provides important security updates and fixes an issue where widgets may revert to their default settings after restoring from a backup."
Given that this is not only a bug fix, but the update also contains security updates, I'd recommend downloading this update as soon as possible.