Some people who use iPhone 6S and iPhone 6S Plus report that they found problem with their phone Wi-Fi connection. Some of them cannot connect to a Wi-Fi at all. They could not enter to the web page completely because there is no Wi-Fi connections.
Some others iPhone 6S and iPhone 6S plus users report that their phone Wi-Fi can connect but the connection is not stable and it disconnected randomly at times. Sometimes they could enter the web page and surf normally but suddenly the connection drops by its own. This connection could drops frequently without any clear reasons.
To overcome this problem, you can take one of some options as the following explanations. You can try the simple way to fix your Wi-Fi connection problem by toggling off and on again the Wi-Fi or toggling off and on again the Airplane mode. Please swipe up from the bottom to open the control center to toggle the settings.
You also can try to hold down the Home together with Sleep/Wake button for ten seconds to reboot your device. This action is often works but it just for contemporary solution.
Other option to overcome your Wi-Fi connection problem is by going into Settings, then tap Wi-Fi, select the problematic network, and please tap Forget this Network and tap Forget. After you take those steps, please back to Wi-Fi page and please set up a fresh connection.
You also can try to reset your phone network settings by taping the Settings, then tap General, and please tap Reset, then please tap Reset Network Settings.
You also can try to change your channel router. If you can connect to a 2.4 GHz connection, you can choose it rather than use 5 GHz connection. Or if you already use the 5 GHz connection, please change to a 2.4 GHz connection instead so that you can see the difference between connecting to both of them and choose what you really need.