Properly configured, it is less about the platform and more so about the server and your connection to it. Servers with SSD hard drives have a faster seek time. Your cable internet will be faster than a data connection in the middle of nowhere.

PHP platforms are the most abundant in the ecosystem, such as Magento, WooCommerce, Opencart, etc. Meaning it will be easier to setup a sever that would run it. These tend to lean on caching their data/pages to make their page loads faster.

You could go the route of a precompiled language like python and use Django which has several e-commerce platform options. It may take more effort to find and setup a server for it though.

Speed also will depend on how visually heavy the pages will be. If you don't use images/css/js it will be faster.