For me, there aren't any cars sub £15k that I'd sell my Edition 30 for. But, there are a few £20k cars I would, my list woud be:
Audi S3 (8P2 Shape) S-Tronic
Focus RS MK2
BMW 135i Coupe
Evo 8/9 (Well specced and low mileage for £15k, then use the remaining £5k for a daily and to sub high maintenance costs)
Golf R (Would be a wait until prices drop to £20k)
Discuss...