Pairing watch
Can I pair I watch 7 with iPhone 7,
which is the min iOS needed in the iPhone to connect with watch series 7
iPhone 7, iOS 15
Question marked as
If the Watch still has OS 8 on it then you can pair with a Watch on iOS15
If the Watch has been updated to OS9 then you need a phone with iOS16, ie iPhone 8 or newer.
The Watch Series 7 originally had OS8 on it but there is no way of knowing if the one you are considering has been updated.