I could suspend my disbelief enough for ghosts and the like, but this is a bit farfetched. A 15 year old just living completely alone, probably coming from another city? If I squint enough and the story is good enough I could suspend my disbelief for that as well, but I still dislike this trope a lot.
But that justification for why the ghost lives there is so stupid. They just so happened to have 400 years old wood good enough for construction? Wood that was literally on fire? And then shipped it over to Japan for building a "designer mansion"?
The premise could have been mildly interesting, but would work much better with either an adult protagonist, or havung the guy live in some apartment, or bring his family along, just as minor side characters