15.6.1 - How long does the latest update take?

To download? Or, to download and install?

Assuming an average Internet connection at your home, it might take 5-15 minutes to download the software.

It might take another 5-10 minutes to install the software and then restart your phone.

That differs. When your network connection is good it goes faster when it is bad. I can only speak in my opinion: here it took about 15 minutes for all, download and install. I have an iPhone 13