Replicating actors can take time. The engine does its best to make this as efficient as possible, but there are a few things you can do to make this job easier.
When gathering actors for replication, the server will check a few things like relevancy, update frequency, dormancy, etc. You can tweak any of these checks to affect performance. When thinking about making this process as efficient as possible, it's best to prioritize in this order:
Don't mark properties to replicate if they aren't absolutely necessary. It's best to try and derive state from existing replicated properties when possible.
Try to take advantage of the quantization functionality that already exists. e.g.
FVector_NetQuantize. These will greatly reduce the size needed to replicate this state over to clients, and if used properly, shouldn't cause any noticeable artifacts.
FNames are not generally compressed, so when you are using them as parameters to RPCs, keep in mind that they will generally send the string each call. This can be a lot of overhead.