Optimization of ShadowDepth in foliage hard scene with dynamic lightning Lighting

m am working on game, style of which is pretty based on stylized foliage, i built some forest, but sadly it has around 40fps on middle and around 70 on low settings. Most of GPU rendering time takes ShadowDepth, i think it’s because of giant amout of foliage combined with dynamic directional light. What are best ways to improve performance and optimize shadows?

Directional Light must be dynamic, if only you don’t have better ways to lit scenes with dynamic day/night cycle and custom weathers, i really would like also your opinion about my decision while making all of this, im newbie in rendering and graphics pipeline.

Update: After some experiments, i found out, that different settings make different problems
Low settings:

High settings: