Q: I have an iphone 6s running ios 9.2.1 my wifi disconnect and after few seconds it reconnects it happens most of the time help me out thanks !

This sounds like you have a complicated name for your WIFI apple products prefer alpha numerical with no spaces.

Is this misbehavior new? If so, what event immediately preceded its onset? Update iOS? Anything at all? Environment (interference)?

I have seen a couple of threads similar - I cannot find them as I did not participate and my search attempts have been futile

If this happened to me, I would:

1. unplug my wifi router for 30 seconds+
2. plug it in and let it cycle up
3. restart my iPhone > Restart your iPhone, iPad, or iPod touch - Apple Support
4. test
5. if NO joy - "Forget" the network and rejoin it
   Go to settings-->wifi.
   Click on the blue arrow on the right of network you no longer want to connect to.
   Click on the"forget this network" button
        This button will not show if you can't connect to that network.
   Connect to Wi-Fi on your iPhone, iPad, or iPod touch - Apple Support
6. test

let us know