TThe iOS on the iPhone 6 plus is 8.3.1 and the iOS from the iPhone 5s is 8.3.
The only reference I can find to 8.3.1 is for a jailbreak. Sorry we that iOS version has not been released by Apple yet.
Apple security updates
https://support.apple.com/en-us/HT201222
It could be a developers release but either way that is not a supported iOS
Good Luck
Where did you get 8.3.1, Apple did not supply it.
IOS 8 versions. 8, 8.1, 8.2, 8.3, next will be 8.4
I recently got an iPhone 6 plus and I'm trying to restore a back up from my iPhone 5s. It states that the iOS is old on the 5s and therefore it won't allow me to restore. What can I do ?
