Lags when dividing a scene into 2 scenes

I need the front scene (arms, machine gun, and the rest) to be rendered on top of the other. The solution is to divide the external world and hands with a machine gun into 2 scenes, this is how it looks:
But now a problem has arisen, namely: when I look at an enemy who has the same weapon in his hands (the weapon in the hands of the enemy is cloned) as mine, the FPS quickly drops, which can be seen on the following 2 screenshots:
The same weapon:

Other weapons:

I guess it’s cloning, you need to clone something at a low level, but what exactly? Maybe my guess is wrong, but then what?

I solved the problem. It was required to separately clone the weapon material, because both weapons had the same material reference.
Here is the code with the solution: