I have no experience of the above unity octane intergration, how ever two of us at our firm have written an octane to unity exporter so we can quickly get octane scenes, geometry, materials and lights to VR devices supported by unity.
Getting the geometry into unity at the wrong size was devistating on unity lightmapping times, as was getting overly high HDR values on emissive unity materials.
For what it's worth, if this is happening I can see you would have a serious slow down on the unity side.