My new iPhone 6S has slow WiFi

Below are some general suggestions for Wi-Fi issues, maybe one of them will help.

1) Perform a Forced Restart: Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears. Allow device to restart.

2) Reset Network Settings: Settings > General > Reset > Reset Network Settings. Rejoin the Network again.

3) Reboot Router/Modem: Unplug from power for 2 minutes and plug again. Update Router Firmware (check manufacturer’s support website for a newer FW). Also try different bands (2.4 GHz and 5 GHz) and different bandwidths (20 MHz recommended for the 2.4 band).

4) Change to Google's DNS: Settings > Wi-Fi > Click on the Network, Delete all numbers under DNS and enter 8.8.8.8 or alternatively 8.8.4.4

5) Disable device prioritization on the router if this feature is available.

6) Determine if other Wi-Fi devices on network are working well (other iOS devices, Macs, PCs).

7) Try device at another Network, i.e., neighbors’, public coffee house, etc.

8) Restore the Device (ask for additional for details if desired).

https://support.apple.com/en-us/HT201252

9) Go to an Apple Store for hardware evaluation.

In my case the problem was that my router somehow kept dropping the IP address binding to the iPhone. Once I changed the setting from DHCP to static, things seemed to work fine. Will see how it manages for the next while.

The later iPhones support AC wireless which is the fastest standard at the moment. This issue wouldnt be with the phone, but more with what you WiFi router or access point can handle.

To rule out.. Restart the iPhone to see if it improves once restarted.

Maybe then disconnect from the wireless, forget the network and re-add/join.

This guide should help a little:

http://www.iphonehacks.com/2015/09/fix-ios-9-wifi-problems.html

You iPhone supports up to AC but will support the previous standards of G/N etc.

On your wireless router or Access Point you should be able to change the wireless settings to specify what range of WiFi is used (G/N/AC). If its supports AC 5Ghz then select this or if not select the N standard. If not you could potentially upgrade your Wireless router or Access Point to a later model which supports the faster wireless.

If you cant change the settings for the above maybe change the channel of the wireless router or Access Point to another number (1,3 or 6) as the wireless may be getting interference from something else.

Also the speed responses you are getting will be your internet speed setings based off what broadband speed you pay for off your ISP and also based on the contention ratio (how many other people are using the same provider in your area)