WordPress - Checkout Page Slow and Site Speed Optimization

Regarding WordPress tasks for [login to view URL], here are the specifics: 1. Checkout Page: I've noticed that when I input all the delivery details and select either Razorpay, CCAvenue, or COD payment options, it takes more than 10 seconds for the page to display either "razorpay" or redirect to the "CC Avenue" page. This delay is unacceptable, so I need you to investigate and resolve this issue. Please ensure that "razorpay" loads quickly or that the redirect to "CC Avenue" happens in a timely manner. 2. Site Optimization: I have already installed the "WP Rocket" plugin, but the site's optimization does not meet the "A" grade on Gtmetrix. It's important to optimize the entire site ([login to view URL]) and server to achieve loading times of less than 2 seconds. Currently, the Gtmetrix score is an "F," and it's imperative that we bring it up to an "A" grade for all pages, not just the home page. Note: 1. Please make the above changes using the "child theme [login to view URL]" (if applicable). Please avoid touching the parent theme or any plugins. 2. I have more changes and more enhancements related to website design. So, I need a person who is a good in WordPress expert as well as a designer.