For the most part, iOS 9 is stellar. It’s rock-solid, and although there aren’t a lot of bells and whistles with this iteration, there is enough to get excited about and the upgrade is definitely worth it.
Unfortunately, some users reported an explosion in data usage after upgrading, which led to a nightmare scenario — costly overage charges and throttled data speeds.
This is all due to an auto-enabled setting in iOS 9 called Wi-Fi Assist. On paper, Wi-Fi Assist is meant to keep your connection stable even when you run into issues with Wi-Fi speed or coverage. When your Wi-Fi flakes, it uses your LTE or 4G connection as a backup. The risks with this are obvious.
Here’s how to turn it off: Settings > Cellular > Wi-Fi Assist.
Simply toggle the button to disable the feature.
If that doesn’t solve your data-gobbling issue, the most likely reason is that apps that normally didn’t use cellular data on iOS 8 have been toggled to use it in iOS 9.
Here’s how to fix that: Settings > Cellular
Apps which are mostly used at home, like Netflix (or other on-demand video services), should be disabled because they often use Wi-Fi anyway. This will dramatically cut down your data usage. In fact, you can even toggle everything off, then toggle apps back on as you need them.
Do you find you’re using more data after updating to iOS 9? Did this help? If not, what was the culprit?