Thanks for using the Apple Support Communities. If you are having issues with the connection between your iPhone and your Wi-Fi network, you may find the information and troubleshooting steps outlined in the following article helpful (it is primarily aimed at "no connection" issues, but the steps listed may still be applicable for slow or impaired connections as well):
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support
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Question: Pictures sent over wifi..why is it slow?