Notice that not every raymarching shader you find is optimized or even has a practical use. With clouds you don’t necessary rely on sharp features so you can upscale a lot, rendering in a lower resolution. If it is practical for your case depends on various things, such as what your target platform is, what your projects target audience devices specs are in average etc.
There is always a cheaper approach too, if you look around here for example one used just billboards still giving a good result.