the first log is almost empty, while the second log shows that you have finished the memory:
In the second screenshot, VRAM is not finished, but Out-of-core is already active, and this is strange.
Probably you have reduced too much the GPU Headroom, please, bring it back to 300/512MB.
To keep the polygons count low, it is very important to enable in c4d the Render Instance, or Multi Instance (R20/R21) option for all the objects that support it, like MoGraph Clonerrs, Instance Objects, or Particle Emitter.
To keep the polygons count low, another trick is to disable all the Subdivision Surface objects in the scene, and apply to them an Octane Object tag, with the same subdivision settings in the proper tab.
In this way, the subdivision will be applied only at render time, and the scene will be much easy to export and handle.
About KitBush 3D scenes, unfortunately default KiBash 3D elements are wasting a lot of VRAM for textures, and must be optimized.
The first thing to do is to go to Live View , menu Materials/Octane Texture Manager, and select all Roughness and Metallic textures, and change their type from Normal (full RGBA) to Float (one Grayscale channel).
In this way, those textures will consume only 1/4 of VRAM, compared with the Normal mode.
To save more memory, you can also completely remove all the Black Metallic 4k textures, and set the Metallic value at 0.
Please check also the Emitter materials, the Texture Emission color is defined by a Texture, instead of a RGB Spectrum node.
Also these textures are useless, and can be replaced by a simple RGB Spectrum node that does not consume VRAM.
Another way to save a lot of memory is to convert all the textures from PNG 16bit, to JPG 8bit, in this way, you can save more than 3x memory.
Finally you can reduce the resolution of the textures from 4k to 2k, but this could have an impact in quality, if you need to see the textures very closely.