If you run with mpiexec in 2015 and 2014, the behavior is more or less exactly the same. To get optimal performance you always need to know what you are doing regarding the parallelization, and we are working on better guides, esp. for the new options in 2015.
The ParallelScheduler is an advanced option which requires quite deep knowledge, and is not related to the usual operation of running a script in parallel. It can be used if you for instance inside your script have 4 tasks to be done, then you can parallelize them.