The question seems noob, but give me a moment, because I should know something about these things.
I am rendering a semi large architecture outdoor scene with buildings and nature surrounding it. The scene has 1.6 million vertices and I use Grow3D (https://www.thegrove3d.com/) and Graswald (https://www.blendermarket.com/products/graswald) addons to generate nature. I have multiple renderlayers with samples from 150 to 400. I use denoising feature.
If I render the scene using GPU with render size of 1920x1080px and with percentage scale at 200, the whole scene renders in 1 hour and 8 minutes. (Memory conception is 1.2GB).
But then, if I increase the percentage scale to 300, computers CPU gets noisy and rendering time increases remarkably. The rendering time estimation shows something from 8 to 10 hours.
And if I take a look to my task manager, the GPU conception bounces only from 0 to maximum 10 percent.
So could there be some hardware limit which I am reaching, or do I just forgot something crucial?
Windows 10, Inter Core i5-7600 @3.5GHz, 16 GB RAM, NVIDIA GeForce GTX 1070 and Blender 2.79.
EDIT 18.9. Here is the link for project file: https://drive.google.com/drive/folders/1n5LKe6f5JNSsUuAUfwsZo6PrfdE0Kk0f?usp=sharing
Because of the link won´t be valid for too long, I will post images about the settings when reason for odd behavior is found.