Updating to iOS 17

I have an iPhone 12 with the latest software update (16)

No, the latest update for the iPhone 12 would be iOS 17.5.1. But, no need to update the iPhone 12 at this time. If you update the iPhone 12 to iOS 17.5.1, the iPhone 15 may not be updated to that version yet, and you won't be able to transfer data from the iPhone 12 to the 15 unless you first update the iPhone 15 to iOS 17.5.1.

Here is what I would recommend:

First, make a backup of the iPhone 12 on iCloud or a Mac

Then, set up the iPhone 15 and transfer the data from the backup of the iPhone 12 over to the iPhone 15 during the setup process

Set up your iPhone or iPad - Apple Support

Once the iPhone 15 is up and running, you can update the software on the iPhone 15 as new updates become available.

Waterlyfe_isbliss wrote:

I have an iPhone 12 with the latest software update (16). However, I just purchased an iPhone 15 and will want to upgrade to iOS 17. What type of additional backups will I need to do?

What do you mean additional backup?