home pod connects for 15 seconds then goes off

If you’re using an Apple TV 4K then you need to set it as the default speaker: Set up home theater audio with HomePod or HomePod mini and Apple TV 4K For other models use AirPlay.

If it’s disconnecting:

• Force-quit the app you were using and Restart Apple TV and restart HomePods.
• Reboot the wifi

If HomePod or HomePod mini isn't responding - Apple Support

Connect to what? Is this AirPlaying music to them? If so from what app?

Are you asking them to play music?

They become unpaired?

Or is it for something else. You haven’t provided enough details to help isolate the issue.

Please provide more details. What were you trying to do with it? This could mean a number of things