If you do not have unlimited data on your iOS device you will want to turn off Wi-Fi Assist in iOS9. Wi-fi Assist uses your data connection when you are on a slow Wi-Fi network.
To turn it off go to Settings > Cellular > Wi-Fi Assist > Off.
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If you do not have unlimited data on your iOS device you will want to turn off Wi-Fi Assist in iOS9. Wi-fi Assist uses your data connection when you are on a slow Wi-Fi network.
To turn it off go to Settings > Cellular > Wi-Fi Assist > Off.