This book is complex enough in each chapter that almost any part could be considered equally "easy" to do a 15 slide presentation on, it just depends on what information you are interested in focusing on.
If you have not yet read the entire book, if I was your teacher I would probably encourage you to do your presentation on the first chapter. This way, you can include a lot of the background information that is necessary for full understanding and appreciation of the entire book. 15 slides will be easy to fill if you keep each slide straightforward and focused on only one main idea. When any teacher introduces a new novel to the class, some basic background information is usually provided. Perhaps think of your presentation as an introduction to reading this novel.
Though it will require some extra research, I encourage you to introduce the author of the book, and some basic facts about his life and writing. Also, you could discuss the reception of the book, its popularity with the general public as well as the response of critics. It would also be a good idea to present the setting of the bulk of the story and give some information about the politics and history of Kabul, Afghanistan. You could briefly introduce each of the main characters and provide the background details necessary to understanding their culture, and how it differs from yours.
A few final tips: Remember that PowerPoint presentations are meant to be a visual enhancement to a presentation, and therefore do not contain every piece of information you will speak about (you don't want to be reading your slides to the class). Make things simple and clear. Use pictures and graphics where appropriate, but don't let them become distractions. Try to identify the 4-5 most important ideas or points within each subtopic, and you'll have a great start.