Optimization of handling many actors with physics.

I’m new to unreal trying to develop a tiny project which contain dense actor(ball) array. Each ball is simply a ball static mesh actor duplication.
After a quick level design I got a problem.

These actors are not so many but too dense to run smoothly, the actor call count eaten up performance.
Soon after this problem I tried Instanced static mesh actor, which can significantly boost performance, but in vain. This is because I needed actors to simulate physics but instanced meshes cannot simulate physics.

How can I solve this problem?