How can the Solutions Architect improve the network speeds between the control instance and the instances in the placement group?

Explanations:

Terminating and relaunching the control instance in the placement group is unnecessary. Moving the existing instance is simpler and does not require relaunching.

Using private IP addresses can improve security and reduce latency, but it does not increase network speeds between instances inside and outside the placement group.

An Elastic Network Adapter (ENA) is beneficial for high network throughput, but it does not impact network speeds between instances inside and outside the placement group.

Moving the control instance inside the placement group enables it to benefit from the same high-performance, low-latency network speeds as the HPC cluster.