I tried to create a cloud filled in the box geometry, I tried using raymarching with noise texture as well direct noise function and fbm – fbm motions is good. but cloud is not get proper result like distorted also frame rate is dropping to 10 to 14, I tried to arrange array of sphere that made to even worse app breaks because it had more than 2000 sphere shapes.

Is there any better way to create 3d cloud shape even pre-calculated is fine but rendering time should have render min with frame rate of 60. Also note scene is big space. camera is at 0, 0, 100 and I need to place in box in -65 with size 400,400, 10 that size will be decided by user for now I trying to 400, 400, 10

I am new to shader so help me with details and point me right direction so that I can work on this. thanks a lot.