some rebuilt or remanufactured turbos are shoddily made and thus some garages will prefer to avoid them,
A new, genuine, K03-073 is around £600. You could have yours rebuilt for maybe half of that. I guess its upto you to decide if thats worth it or not.
K04-015 is essentially no different to what you have now. It was designed as an upgrade for the old K03-005 used on the original B5 150hp engine, and the K03S fitted to the 190 BEX engine has the same compressor as the K04-015 has, albeit with a slightly smaller turbine.