Apple's iOS 15.4 update could have a huge impact on your iPhone's performance. While some users should install the new firmware now, others are better off waiting a few more hours or maybe even days before upgrading from older iOS software.

iOS 15.4 is the latest update for iPhone and it is available to download now if you own an iPhone 6s, iPhone 6s Plus , iPhone SE , iPhone 7, iPhone 7 Plus , iPhone 8, iPhone 8 Plus , iPhone X , iPhone XS , iPhone XS Max , iPhone XR , iPhone 11 , iPhone 11 Pro , iPhone 11 Pro Max , iPhone SE 2, iPhone 12 mini , iPhone 12 , iPhone 12 Pro , iPhone 12 Pro Max or an iPhone 13 model .

The iOS 15.4 update is a major upgrade and brings a bunch of important new features, improvements, bug fixes, and security patches to iPhone owners around the world.

iOS 15.4 requires a fairly large download. That's around 1.25GB for iPhone 12 Pro owners moving their device from iOS 15.3.1. It should be about the same for other devices.

That being said, it might be more important for those of you who are upgrading from older versions of iOS. This is because the features and fixes from the updates you skipped are rolled into your version of iOS 15.4.

Those of you who have trouble with older versions of iOS might see a huge turnaround after installing iOS 15.4. We hear about positive changes. That being said, we are also hearing about various bugs and performance issues.

If you've upgraded to iOS 15.4 and can't stand its performance, note that you can't downgrade to older iOS 15 software. Apple has stopped signing on iOS 15.3.1.

Unfortunately, the path back to older iOS software is also closed. This means that those of you with excellent experience on iOS 15.3.1, iOS 15.3, and older iOS software should approach the iOS 15.4 update with caution. Once you've made the move, there's no going back.

Initially, it looked like Apple would allow iPhone users to stay on iOS 14 and receive new software upgrades. It won't, it seems.

Apple hasn't released a new version of iOS 14 for months, and the most recent version of iOS 14 is gone. Devices running iOS 14.8 and earlier can only upgrade to the latest version of iOS 15. There is no way to upgrade to the latest version of iOS 14 (iOS 14.8.1).

This policy is unlikely to change. So if you want to stay on iOS 14, you'll have to be prepared to do so without access to the latest bug fixes and security updates.

If you're currently debating a move to iOS 15.4, allow us to walk you through the best reasons to install the software today and the best reasons to stay on your current version of iOS a little longer.