In order to identify the source of the issue, could you please set up a new WordPress site using DevKinsta and check if it shows the same latency as your custom local site?
Additionally, while your custom local site is trying to load, could you check the resource information of the containers in Docker Desktop to see if the resources are being fully utilized?
You can also check the resource usage of each container by going to specific Container >> Stats.
example:
I hope the above information will help uncover the source of the latency. Please keep us updated on the progress!