Having gone through it and the crushing affects that we eventually ran into on our production boxes, my first step is now to check if the connection strings are MARS enabled.  The documentation, for example, for Entity Framework states that it's off by default.  I have anecdotal evidence that it actually defaults to on.  MARS is for very special, tightly controlled, very well written specialty code.  Since most people's code meets none of those requirements, you need to make sure that it's turned off. 

Also anecdotally, all of those 15 second warnings seem to have simply disappeared after we turned off MARS on all connection strings for all applications.