Whats the problem about snow maps? At this point it´s just a cosmetic thing.
There are some special effects markers that float large fog/cloud textures close to the camera. These textures bog down the GPU very badly.
There are also additional things like drawing the snow in the air, snow on the ground, foot steps, vehicle tracks which all add to the drop in FPS.
Most of the 3v3 and 4v4 snow maps were reworked to improve FPS (except LaGleize). It will be interesting to see if snow maps become more popular after the rework.
A good spot to test on LaGleize is just left of the center VP by the munition. That is where the fog textures are pretty heavy.
But I am always going to ask people about snow maps to verify what exactly bogs them down for all sorts of PCs and hardware.