Look, if you don't want to actually try to fix the problem and just complain about it, go ahead. A lot of people have this issue every major iOS update because a vast majority of iPhone users restore their backup to their phone any time they do a reset.
I have an iPhone 6S and 5c that are both running well without issue. But why believe the people that actually fixed their issue? Why trust the engineers at Apple? Surely some random stranger complaining about phone performance degradation on the internet is more correct than the collective of minds that created the device and its operating system.
If the only thing you or your husband heard at the store was that you needed to buy a new phone, you didn't listen. Just like how you're not listening right now.