Do not use the development http server in a production setting. Use gunicorn or some equivalent.
I had the same issue with incredibly low throughput on beefy machines and it's because the dev server implementation is single threaded and does not do concurrency at all.
Switch to gunicorn.
Better yet, put gunicorn behind nginx, make sure all static assets are served by nginx, add appropriate Cache Control headers. Furthermore understand and use Django’s page caching.