Wi-Fi connectivity isn't always the best way to connect to the internet, and Apple knows it.
That's why a new feature coming in iOS 9 will let your iPhone (or cellular iPad) automatically drop to your mobile internet connection if the Wi-Fi is struggling.
At the moment on iOS you have to manually switch to mobile data. If you're on a poor Wi-Fi connection it'll just keep trying and you'll get stuck with some horrible loading times.
It's a simple enough idea, but neither Android or Apple seem to have worked out a fix until now. If you're on a limited internet package you'll be able to toggle the feature under Settings and the bit called Wi-Fi Assist.
The feature has been spotted inside the developer version of iOS 9, but you can expect it to be in the full version when it launches in September - probably alongside the iPhone 6S.