Causes performance issues when static meshes and foliage are together

when i have a building with the foliage
fps will drop a lot + drawcall will increase a lot

Separately, each of them has little effect on performance
But as long as it is in the scene at the same time, the performance will be greatly reduced
There are also exaggerated proportions of shadow depth

Wondering what could be the reason for this

Because it seems to appear when facing the angle of the sun
I also tried to cut off the directlight, skylight and some light sources in the building, but it didn’t affect much.
There is a distance between foliage and buildings, not staggered and then together