£15K doesn't buy much old Porker these days I'm affraid. Prices have crept up and at that price you might find something that is outwardly quite nice but will probably be a little tired.
£15k buys a very nice 20V ur-quattro or the very best E30 BMW M3 though. Two iconic 80's flyers that are going to get very pricey over the next few years.
My choice for £15k would be to get a couple of the guys round, a crate of ale, a rusted out MG Midget as doner car, a 988cc A- series engine with a vane type Supercharger and a Westfield Eleven kit- lock the doors and get stuck in. Emerge 2 days later with a cracking little sports racer, that will scare grannies for miles around. Should make a tidy little profit when you come to sell on too- which is always nice!