I can speed up most commonly used shopping carts / webshop engines, such as opencart, wordpress+woocommerce, joomla, magento, etc. I need access to the hosting via FTP, the site's backoffice (admin login), and if you can also provide cpanel access, then more speedup is possible.
NOT AVAILABLE FOR SHOPIFY, ETSY, BIGCOMMERCE, or similar sharecrop-based shops.
If your shop was built on the shopify, etsy, or similar "rent-a-shop", or "pay-as-you-go" platform, speeding it up is impossible from the user's or developer's end.
If you really want to have a fast platform, I can set it up for you with real hosting, and real shop engines, like Wordpress, Opencart, Prestashop, and similars that were specifically built for e-commerce.