UPDATE
While connecting, it looks like Tridion iterates through and performs several different Tridion.ContentManager.Workflow.DesignerService.WFListener.GetSystemWideList()
methods. These methods in turn make a database call and read data back as a result of the call.
the final iteration of the GetSystemWideList() method makes the following database call:
TCM_WORKFLOW_GETLIST_PROCESS_DEFINITIONS
While the database call itself take less than 100ms to complete, it looks like the resulting data read takes a whopping 2+ minutes to complete in Sandbox.
I tried browsing Workflow Process Definitions in Tridion Browser. And it take around 2 mins to respond but present the results in the end without timing out.