Hello mjw2185,
Thanks for visiting Apple Support Communities.
It sounds like your iPhone 6 Plus is restarting continually and you're planning on restoring it using Recovery Mode, but wonder about the "Update" option.
If you click "Update," iTunes will try to reinstall iOS without erasing your device. Updating as opposed to Restoring is a good troubleshooting step for a device that gets stuck during start up.
If you still see the same behavior after updating, restoring in Recovery Mode may still be necessary.
You can find this information here:
If your iPhone, iPad, or iPod touch doesn't respond or doesn't turn on - Apple Support
All the best,
Jeremy