Not even getting into the fact that an m5.xlarge has roughly as much muscle as an old laptop.

Get normal disks of a larger size, it comes with 3 IOPS per GB.

"We'd rather not manage the database ourselves" was the answer from the lead dev, and I do understand that: it's not the developers' job to manage servers. In this company, management has removed themselves from anything technical and the devs don't like managing servers, so they say "let's use AWS, we'll write some code once to create our environment and Amazon takes care of the rest" - and by this point they are committed, with months having been spent on getting things running on AWS, changing the code where necessary etc, so reversing it would be a hard thing to sell to investors and the team.