Do everyone a favor, remove all the fire geometry from foliage surfaces (bushes and tree leaves). As far as I can tell, the presence of these hit-boxes doesn't affect gameplay in any meaningful way other than causing a huge lag festival every time weapons are fired outside of a city. This would be the simplest fix. Please do this. It would be extremely easy and solve the issue for good.

It seems like the issue is actually worse after the stable update.