Handle Many Characters that have skinned mesh renderer

hello i need help with something. I've been trying to solve this problem for about 5-6 days. I optimized most things in the game and ı get 60fps on my mobile device (60hz).

My game is a 3D game in the style of tower defense, because of this I add 20-30 characters to scene. But even if I add one characters that have skinned mesh scene renderer fps decrase 15-20fps. I do not think because of material or models because when I add low poly character, I get same result.

when I replace skinned mesh renderer on character to mesh renderer, everything work wells and I get 60fps.

what should i do here?