[singron]

It's very difficult to manage IOPS for RDS. IOPS scales with RDS disk size to a certain point, so you might not have had nearly enough IOPS at only 200GB. It's possible that you used too small of an instance type since you should probably use an instance that can keep all 15GB in memory and incur only write IOPS from WAL writes, bgwriter, and checkpointing.

Even a single nvme ssd can greatly exceed the maximum IOPS available to RDS, so you have to be very careful migrating database workloads to RDS.

Once your workload exceeds available throughout, latency will be terrible.

These are all hard lessons we've learned on our own. Support will not help you if you have terrible performance issues with RDS. They love to tell you to try optimizing your queries. AWS could afford to staff multiple dedicated support positions for our account, but they pocket the money instead and give terrible canned responses. If you have a tiny account, they definitely won't help you. Some people say support is great, but I've never had a good experience.