Yeah, big ticket items can include rust, paint, crash damage, complete neglect, major interior refreshes and of course major internal engine work. To me a head gasket is a medium sized job if that's all it needs as it's not that expensive if you diy and it gives you a chance to catch up on a lot of "while in their items".
Looks like an earlier FZJ if I'm not mistaken with the AFM, ODB1 and earlier transmission, etc. The earlier FZJs are less desirable in my opinion though I know many, if not most, prefer them. All else equal the MAF and ODB2 are worth a decent premium to me. Could be the opposite to you and you may be seeking the earlier version but I wanted to throw this out for consideration in case it helps your negotiations. Knuckle service needed, earlier version and whatever else you care about may move the needle a bit in terms of how you value it.
So many variables but if it seems great and makes you happy as it sits and you can cover whatever curve balls may come up 15k seems reasonable to me.
Good luck