Setting different resolution for pointcloud/rgb from camera

is it possible to set different resolution for rgb and pointcloud in camera? I solved it by creating another camera at the same position with different resolution, but every new viewport is 1500 MB increment on GPU memory.

(I want undersampled pointcloud because sending 2000x1000 big pointcloud at 60 Hz makes rViz unusable - or am I doing something wrong?)
Thank you.