What could be the cause for my high disk IO latency (from sys.dm_io_virtual_file_stats DMV)?
My problem with this DMV is that it misses the critical context of time, so it's difficult to pinpoint when the spikes in latency occur.   If you're running a VM rather than an RDS instance, I'd recommend setting up a Perfmon Trace to collect disk latency metrics so you can narrow down the times.  If that's not an option, push the results of your query to a user table every 5 minutes or so and then trend out the deltas so you can see what periods of time experience spikes.

Once you figure out when spikes are occurring, you'll have an easier time identifying the cause of the latency via Extended Events (e.g. capturing long-running queries), Job History, etc.  Who knows, maybe you've run into a situation where you've got nothing locally directly affecting the I/O during the spikes at which point you need to escalate to Amazon with this information in hand.  Noisy neighbor scenarios happen, so don't rule anything out.

On a side note, if you want to further break down the DMV stats to their database files, check out Paul Randal's post on this DMV explaining how to do that.