Thanks for the feedback. The geometry is subdivided to allow it bend around corners smoothly , but you could create a conditional relationship based on Spline IDs that tells RC to use the high poly object for curves and the low poly object for straight sections. This would be especially important if you're exporting the geometry to a real-time engine. Otherwise, the high poly count shouldn't be a big problem because RailClone instances any segment that is not deformed or sliced, so really the rendering overhead is very low.
If you want to know more about conditional rules in RailClone then the Creating Conditional Relationships
chapter in the Next Steps with RailClone
guide might be useful,
I hope that helps, please let me know if you have any further questions.