A few things.
1. I'm still not feeling anything in this relationship between them, completely apart from any weirdnesses due to age difference.  It just seems like she nagged at him until he gave in and married her.
2. The fact that he's technically an ephebophile instead of a pedophile isn't a huge win.
3. Of course the years lived in his former life matter.  He has the mentality and consciousness of a person in his 30's.  He has enough life experience to be able to take advantage of a teenager, who is far less likely to notice that they're being manipulated, and that's what's really at the heart of whether or not a minor is capable of consent.
4. Obviously he ISN'T taking advantage of her, and she is down to get down.  So that mitigates things somewhat.
5. As others have said, it's a different world with different laws and different expectations.  That changes a lot of the dynamic.  Plus, they're married.  But it's still a little weird to think that 30-year olds can isekai to fantasy worlds and bang all the 15-year olds they want without fear of repercussions.  The fact that they can hide in a 15-year old body to do it doesn't make it less weird.