15K is TOP money for an S1.
The red one is amazingly clean - I love the underside!
My main concern on such low mileage (and therfore little used cars) would be around rubber parts perishing and the few steel fasteners (like on the clams, undertrays etc) rusting and siezing.
All easily fixed.
I have had mine for 12 years / 120,000 miles as a daily driver and still love it.
Seloc is THE place for information, but bear in mind that LOTS of the comments are of the "I can spend LOADS on mine - and you should too" (eg Nitron shocks etc)
As was said, make sure she is happy to get in and out of the car. The sill is high and not terribly conducive to an elegant exit if she is wearing a skirt ....
Find a decent repair place who know what they are doing. They are not complex cars but it is much easier if you know what you are doing.
By the way Geary at Eliseparts (
http://www.eliseparts.com/) is the Sue Miller / Paul Matty of Elises.
Personally, I would go for a higher mileage car that was regularly used and well maintained by one of the "normal" places (Steve Williams, Lakeside, Hanger111 etc).
Regards
Bruce