Lag in viewport when moving the tire, tire treads, tire treads curve.

Hi, I'm currently finished with the tire part. And my viewport is now having crazy lag whenever I try to move the tires/tire treads/tire treads curve or change in the  tire tread modifiers. Moving the rest of the car is no problem. I found that hiding the mirror modifier that mirros the tire treads to the other tires helped abit.

I was just wondering why this happens. Thank you.