Hello shagrat,
I tried your advise and installed GPUz. I applied two different approaches. At first, I maximized the settings as indicated on Pic_2. At this setting, minimum fps is around 10 FPS with mirror is on. Secondly, I decrease clutter and tree visibility as indicated on Pic_1 and got min 25 FPS.
GPUz gAVE 1607 MB memory for first approach and 1637 MB for second. It is interesting that, GPU usege is much more with low setting (Pic_2) than high setting (Pic_1). On the other hand my GPU has 2GB vRAM capacity but it is not use all of them. May be a problem about GPU?