The runtime is not loaded every time. The runtime is only loaded when the cache is cold. For a typical Node.js Serverless function this "cold start" takes about

The runtime is not loaded every time. The runtime is only loaded when the cache is cold. For a typical Node.js Serverless function this "cold start" takes about 3 seconds. After the function is warmed up it is just as fast as if it was on a dedicated server. Unless it cools off. Which it won't if the function gets regular usage. As the function becomes more popular it will be loaded onto more servers and the work can be spread across those as well.