Yahoo Auctions Japan is a deep deep rabbit hole.
Yup, that's a new old stock S15 engine. Not one of the new 2022 production Mercury Japan SRs or a reman. They have a video linked from the auction. Looks like the seller has a lot of NOS items and engines.
https://www.youtube.com/watch?v=lJUjKD6LwpE
Buyee won't let you purchase engines and for some reason also blocks listings for coils/dampers (I guess the gas charged shock is considered a hazard?). But there may be another service that does those. Buyee will ship big stuff like bumpers and exhausts though.