Optimizing Woocommerce's "Add to Cart" function

Adding a product to the shopping cart takes 5-10 seconds which is an unacceptable time killing the conversion. I am looking for a professional who can optimize this function

Problem details:

I have a store set up on Woocommerce. Xstore template. Store installed on a VPS in a Polish server house.

By default, on the Xstore template developer site, the function of adding a product to the shopping cart works perfectly.

When you click Add to Cart, the shopping cart widget on the right side of the screen slides out almost immediately .

On my site, on the other hand, the add to cart process takes 5 seconds with the WP Rocket caching plugin disabled. And about 10 seconds when WP Rocket is enabled.

From what Xstore support writes they just use WP Rocket on their demo sites and somehow the function of adding a product to the shopping cart works instantly on their site.

PS. There is a Payu plugin running on the site, but after disabling it I didn't notice any improvement in the performance of the shopping cart, so rather Payu is not the problem.