The rear anti sway bar doesn't look like 3/4 inch. Ask him to measure it. Also, ask him to turn the steering wheel lock to lock. A true WS6 car will be 2.5 turns. Those two things, along with the correct decal in the door, would point to the WS6 suspension. However, if this originally had a manual transmission, it was a W72 car. It does appear that the engine has been meddled with. And, I don't understand why they would change the air cleaner base. The fuel intake line isn't insulated either. It would be odd for a 72K car to have had some major engine work as this appears to have had. The A/C isn't working either.
This car, in my opinion, isn't worth anywhere near $15K. I, like Brett, would be very leary of the mileage. But it does look like a solid car. Don't expect to buy it and not have to put money in it though. If the tranny hasn't been rebuilt...it's time. Who knows what the engine is like. You'll have lots of supsension issues too. All normal for 30 year old cars.