So, if I got it, the best solution would be to:
1. Recreate simplified room shape with editor's Box and Plane models.
Yes, with invisible shapes (visible = 0 or alpha = 0). visible = 0 will be faster but for debugging you can use alpha=0
2. Sett Collision and Static to 1 (should I also sett Polygon Collision to 0 or leave it empty?).
Leave it empty
3. Place them in a Merge container.
Yes. A separate Merge container for each room.
..and just two additional questions:
1. Is there a big difference between Merge and Group container and can I place Group container inside the Merge container?
The Merge is combining all of the objects into one object. The Group is just grouping the objects under the same father but not merging them into one. With the Group container, you can still move the child objects in game time but with Merge you can't.
We haven't tested Group inside Merge but it might work.
2. For main (non-collision) room geometry (that I placed in Group-containers) I checked Static in both Group container and OBJ models, should I sett 0 to Polygon Collision for all or just leave it empty?
When using static under a Group container, the collision will be the bounding box of the Group and not the subgroup elements.
For the subgroup elements collision, you can check the "Sub Model Collision" inside the Group container.
Regards,
Cyberix3D team