there's actually no HDRi at all in that scene. The light light sources are one sided planes only. Set them to diffuse and then attach a Black Body emitter to them. I set those up in front of the windows (Can't really remember how many windows there are in that room, I think it was 4). Then I selected the window material in Octane (via the material picker in the left upper corner of the rendering viewport) and set the Opacity of that material to 0.0 (basically invisible).
That way the specular material of the glass doesn't interfere with the light, which otherwise would really slow down your render.
I don't really use the script that turns Poser lights into emitters at all and mainly use primitive meshes form the poser props section to light my scenes. Usually spheres, and one sided planes do the trick just fine. (Which is actually what your poser lights are, once you run the script over them - one sided planes