I'd go with the following:
- What is project management? What are the different phases in project management?
- The advantages of project management
- What will happen to a company if it fails to adopt project management
- The different project management methodologies/frameworks (Waterfall/Agile)
- The project management overhead (how much does project management cost)
- The role of the PMO (the Project Management Office) in "managing project management" (in other words, how do we ensure that project management is done the right way)
I think this should be enough material for a 15 minute presentation.