Alright... the 15k is gunna kill my list as well because my top 5 would pretty much all be collectors items that sell for more than 15 but aren't necessarily worth more than 15 (i.e. 93 cobra, 66 mustang fastback and alike). SO, as for my reasonable list... (in no particular order)
88-93 Mustang 5.0 5 speed. Good all-around build (road-racing or drags) and capable DD...
Brand Spankin' New (whatever year that may be) GSX-R 1000. What else are gixxers for - just plain fun, cruising, drags, kneedragging etc...
1995-2003 BMW 540i - grocery/family mobile. depending on the year this would end up right around that 15k mark but since I wouldn't be able to get a V10 M5 I would settle for this
1996 Ford Bronco - lift, flares, tires, bumpers - decent all around off-road build... good for the mountains or the desert. Mild crawling or (mild) pre-running...
and, finally....
An early 70's Triumph, customized cafe racer... maybe this is just a phase I'm in right now, but I reallly want to build a cafe racer. I'd really like a vintage ducati but that would be much harder to come by - I'd even settle for a honda cb750 if i had to...
OK - that took a bit more thought that I would have guessed... but there it is... my current "reasonably-minded-wish-list"