Welcome to Apple Support Communities, AMcCarter8!
Congratulations on the new iPhone 6s Plus. I also see from your post that you're trying to set it up using a backup. But iTunes seems to be be stopped estimating how long the completion time is. I'll be glad to help.
Since you're setting up a new iPhone, it's all right to disconnect it from your computer. Restart both the phone and the computer and when your computer is back to the home screen, make sure iTunes is up to date. Get the latest version of iTunes -- Follow the steps under "Mac" or "Windows".
When you're certain iTunes is up-to-date, check your iPhone 6s Plus' screen to determine whether you're seeing the home screen or the "Connect to iTunes" screen.
If you see the Connect to iTunes screen on your iPhone, iPad, or iPod touch -- Follow the steps in this article if you're seeing the "Connect to iTunes" screen.
Restore your iPhone, iPad, or iPod touch from a backup -- Otherwise, restore your iTunes backup to the iPhone 6s Plus to set it up.
Let me know how it goes and have an excellent day!