The first call to our API is always extremely slow. For example, below demonstrates the CPU usage and time it takes for the first call to complete:
Not sure if anyone has addressed this yet, but I've learned about some performance issues arising on the initial startup of Entity Framework. Julie Lerman discussed this in her Pluralsight course on Entity Framework, and is also alluded to in the following article excerpt from Microsoft:
One of the biggest drags on performance is the startup time involved with the first use of a context in an application process. You can do a lot to improve that startup time, though. Hopefully you’ve already learned these tricks from my own writing or other resources, such as the MSDN doc on performance considerations at bit.ly/3D6AiC.
A startup step that often hampers performance is the view generation of mapping views, where EF creates the relevant SQL to query against each of the entity sets in the model. These views get leveraged as your app runs so that for certain queries, EF doesn’t have to work out the SQL on the fly. View generation happens whether you created your model with the EF Designer or with Code First. You can pre-generate these views and compile them into the application to save time. http://msdn.microsoft.com/en-us/magazine/dn532202.aspx
Here it seems she's not just talking about the 'initial load' but the actual first use of a context. I'd to a quick search for Julie Lerman and Entity Framework performance issues. I noticed similar slowness when making the initial calls to my Web API. Every call after the first was significantly faster. I personally haven't found it to be too awful, so I'm ignoring it (for now). However I do find it interesting that it doesn't occur in debug mode. Sorry if you've already explored these options, but I hope this helps a little.