15" wheels would only looks good if they had a VERY low profile tyre on them, with lowered suspension. which would all mean pulling and rolling the wheel arches.
just adding big wheels to a car and not lowering the suspension always makes the car look likes its got 4X4 suspension! the car would appear very high off the ground.
like slater said. try looking for some 14" allows from a VW polo or Golf (mk1 and mk2 golfs/golf gti's mainly came with 14" wheels).
dont forget to check the offset/ET is you are getting some wheels!
mike