very slow when i proceed with checkout

Hi!
I have a similar problem like this: https://www.ads-software.com/support/topic/checkout-pages-loads-very-slow/ but I could not fix it as there says. (I have no JS errors)
When completed the purchase becomes very slow. the site goes fast at all times, only it gets slow when trying to pay. Renaming folders to see where was the problem (discard the theme or plugins) I realized that the problem is with the file /wp-content/plugins/woocommerce/includes/gateways/cod/class-wc-gateway-cod.php . when you rename the speed problem goes away.
From WooCommerce settings delete this payment method and enable others and the problem disappears.
it is only when cash on delivery is active.
The link: https://sillasymesasfabrica.com.ar/
So many tanks!