CircleCI does not inherently throttle network speeds, so there may be an outside service or upstream component affecting your builds. To ensure you don't hit slower network speeds we recommend placing any relevant infrastructure you need to communicate with in the same region. Executors are typically run in AWS us-east-1, us-east-2, and GCP us-east1, us-central1. You can find more information about this on our IP Ranges documentation page:

https://circleci.com/docs/ip-ranges

If you're seeing signs you're hitting slow network speeds: As a next step, consider if the VPN vs No-VPN test is right for this instance:

See How to set up a VPN connection during builds