How to speed up render?

Dear vtk users:
15million points cost 1.8s to render. Is there any solutions to accelerate render ?
Here is my code
renderdemo.cxx (1.7 KB)

1.8s does sounds high to me but note that the first frame necessarily includes a lot of extra setup cost.

What do you get for subsequent renders? I.e. add a loop that spins the camera and renders. Those will be faster and are often more representative of user feedback experience.

Thank you very much for your kindly reply!
Actually I operate on a depth img, and need to manual crop diffrent area of the depth img to render each time,cropping operation changes the rendered data every time.