Apple Watch pairs with phone but unpairs automatically after about 15 seconds. It won’t stay paired. What could be the problem

Hi Msproblem,

Thank you for posting in Apple Support Communities!

Since noticing this, have both your iPhone and Apple Watch been restarted? Restarting our device can help when we're experiencing unexpected issues such as what you are experiencing.

To restart your iPhone:

1. Press and hold either volume button and the side button until the power off slider appears.

2. Drag the slider and wait about 30 seconds.

3. Press and hold the side button until the Apple logo appears to power it back on. Once back on, test to see if this continues.

Check out: Restart your iPhone - Apple Support

To restart your Apple Watch:

1. If your Apple Watch is charging, take it off the charger.

2. Press and hold the side button until you see the power button  in the upper-right corner of the display.

3. Tap the power button.

4. Drag the Power Off slider.

5. After your watch turns off, press and hold the side button again until you see the Apple logo.

Restart your Apple Watch - Apple Support

You should also confirm that both device are up to date running the latest version of iOS and watchOS.

Check out the following resources:

Update your iPhone or iPad - Apple Support

Update your Apple Watch - Apple Support

If this continues after following those steps, you'll want to work with Apple directly for further assistance.

Depending on your region, you may be able to reach them here Get Support.

Take Care!