Using a grain brush on large format makes the file size to large

Hi everyone,

I'm working on a large mural 2.40 metres on 15 metres. I wanted to use a grain brush on my illustrations, but because of all the single dots in the brush, and the brush is used on a big size, the file gets really big like 350 MB and illustrator gets slow and shuts down so I can't finish my design. I tried using the grain filter, looks fine from a distance if you print it, but if you look closer it is pixelated and that is not an option because the mural is situated in a narrow hallway so people will look at it very close. Any ideas how I can solve this problem? Many thanks!