If the reduce polygon tool in Softimage leaves gaping holes in your mesh, that's probably because you have unconnected edges/duplicate vertices.
That said, the tool is actually pretty good - my only complaint is that it doesn't leave smooth edgeloops, but since SoaSE ships aren't animated, that's not much of a problem.
If you need more flexibility as to which areas of the model will get reduced and which will not, use a weightmap, just remember to attach it to the model BEFORE you apply the polygon reduction tool.
Oh, and you also get much cleaner results if you tick the "Preserve Quad Lines" option - provided your original model is composed of quads, not tris. Since you're using extracted models from EvE, my guess is that's not the case.
And finally - Moros is a curvy ship. There's a reason it is high poly. Curves need a lot of polygons. So there's a limit as to what you can do, regardless of the technique and software you end up using. It's a game model for a MMO featuring sometimes thousands of ships on screen, and as such you can bet the CCP developers made sure it is as optimized as it can be. 15000 polys sounds about right for that model.
