First-- what you're really testing here is the Jackson library. A majority of the cycles used in your application are being burned in that toJson call of an array of objects. This isn't a fair test compared to the servlet implementation because you're calling Jackson against a map in the Play example, versus against a simple String in the servlet example.

Second-- you are running database calls serially, and those are blocking. Considering that you're using the more-or-less default Play/Akka configuration, there are only enough threads as you have available processor cores. I would start by increasing the parallelism-factor and parallelism-max to be higher, so you'll have more available threads. More importantly though, the database access should be wrapped in a Future, and you should be returning asynchronously. This should speed up the application by a huge amount.