@allan.sene, is your RocksDB very large? This is likely a symptom of a known issue where Dremio takes a long time to access those system tables (which are basically a sources on the coordinator node). We are currently trying to address this through code changes.
Try building a reflection on each of those tables to see if you can accelerate the query that way (if you can create the reflections, then Dremio will not have to go to RocksDB for the dataset)