Using a particle system can be computationally expensive, especially when incorporated into a full 3D scene. Sometimes that’s unavoidable and render times just have to take a hit, but in many situations you can get away with doing it in post. This will depend on factors like objects in the scene or camera placement, but if you can get away with it, turning to something like Fusion or After Effects can be a real time-saver, and even a little easier than the best 3D software like Houdini or Maya.
Snow is a hard effect to achieve, it's much more difficult than adding rain, for instance, as it has more detail and density, both in the flakes you use as particles and in the motion itself.
