Does the Apple Watch (new serie 1) couple with iPhone 5 iOS 9? I am running my iPhone 5 with iOS 9.  This setup is already slow and I don't want to update to iOS 10 to make it slower. I'm also considering buying the cheaper Apple Watch which needs tethering to my iPhone to access locations, etc.

Could there be any problem with an iPhone NOT running iOS 10 with an Apple Watch?
According to information I got from Apple watchOS3 requires iOS10.