Impact on using single RDS for both Application DB and Temporal DB

We have a AWS RDS instance, that holds a DB with customer data in used by our custom application. If we were to use the same RDS to host temporal and temporal_visibility DBs, what will be the impact on CPU/memory/storage?

For storage impact, we realised that using low retention period would help.

Please suggest what configs, can help in such a scenario so that our Application is having to fight for resources with Temporal. It is okay for our use case if Temporal runs a bit slower as a sacrifice.

Thanks in advance!