iOS 15 on iPhone: Two features you should definitely turn off

Generally, iOS updates go smoothly and there’s little to classify as “critical.” However, iOS 15 includes a new option (and retains an old one) that you’d better disable in most cases, as they can quickly consume your mobile data.

Disable Wi-Fi Assist

An older feature that still remains active for some people and consumes mobile data is the “Wi-Fi Assist” feature. The idea behind it is good: it ensures that your iPhone switches to mobile data when the Wi-Fi connection is poor, allowing you to benefit from better internet speeds.

However, if you don't have a data flat rate or a large data package included in your mobile contract, you might quickly use up your entire data allowance for the month without even realizing it. You might think that you're always on Wi-Fi at home, but with this option, you can easily switch to the mobile network just because you're starting the washing machine in the basement.

My recommendation is therefore to disable the 'Wi-Fi Assist' option. You can find the setting by going to Settings > Cellular > Wi-Fi Assist (Note, the option is at the very bottom of the Cellular page, and you have to scroll past all installed apps first!).

Disable backup over mobile data

The second feature, which is only available for 5G iPhone models (iPhone 12 and later), is called 'Backup Over Mobile Data'. It's not hard to guess what this does: The iPhone occasionally creates backups and usually sends them to the Apple cloud only when the device is logged into Wi-Fi.

With iOS 15, the option was added for the iPhone to send a backup to iCloud over the mobile data network. This can be useful if you don't have to watch your data usage, but for those who – like most people in Germany – have a limited data package per month, it's better to disable this option.

A full iCloud backup can quickly take up 20 or more gigabytes, depending on the storage space on your iPhone – which would more than exhaust the data allowance of most mobile contracts. Once the backup is in the cloud, the iPhone only uploads smaller amounts of data because it only updates changes to the data, but even then, you can easily use up a gigabyte per day.

Under Settings → Your Name → iCloud → iCloud Backup → Backup Over Mobile Data you'll probably find a green switch. You should disable this (set it to gray) so that no data is used for iCloud backups in the future.

It's also unclear why Apple has this option enabled by default. In the description text under the feature, they themselves write that enabling this option can lead to faster-than-usual data usage.