Speed-up REST API call for client residing on a local network

I have a REST API server and client (both on Docker containers, if that matters) residing on the same local network. Each HTTP call to the API takes 500ms to 1 second. This is acceptable however as soon as the client makes 3 or more API requests for a single action, the slowness becomes noticeable. This is using local IP as endpoint btw.

Given that both client and API is just “local”, is there a way to speed this up (aside from client-side caching)?