Other issues like high ping or latency have often been reported by the users of the phone. The most common reported iPhone 6s Wi-Fi issues are...

Wi-Fi gets disconnected on iPhone 6s.

Wi-Fi stays connected but there is no internet on the receiver.

Slow Wi-Fi speeds on metered/ non-metered connections on Wi-Fi.

High Latency/Ping on Wi-Fi connections

iPhone fails to connect to Wi-Fi

iPhone can’t discover your Wi-Fi connection.

These Wi-Fi issues found on iPhone 6s are pretty common issues found on other wireless supported devices too! And does not necessarily indicate that there is something specifically wrong with your iPhone 6s wireless hardware. There are some DIY (Do it yourself) fixes available for your smartphone in this case.

Check your wireless router. Unplug it from the power source for 10 minutes and try again and see if the issues have been resolved.

Turn your Wi-Fi off for five minutes and try again.

Forget and reconnect your Wi-Fi connection.

Restore the default network connection

( Reset from here: Settings > General > Reset > Reset Network Connections > * Enter Passcode * > Confirm)

Update your iOS to the latest version available.

If none of the solutions mentioned above works to resolve your Wi-Fi issues on your iPhone 6s, you may need to get it checked by a professional technician.