The GET /inventory/items call is one of the slower calls in the check-in/out workflow and RTAC tests. Run the test with 1, 5, 8 users for 30 minutes to see if there is anything to optimize in the database or in the code.
This is a simple call that goes through a couple of layers: mod-inventory, mod-inventory-storage, and database. It'd be interesting to get the average time of executing the SQL query vs. the overall response time.
Need to profile this call.