This is a question I see and hear a lot but unfortunately there is no set answer. While I use less then 15 on mine (including 2 extras for premium versions), you may need to use more. You may even be able to use less. Best rule here is to go with what you need for desired functionality first. Less is more when it comes to plugins. Different themes offer different customizations. Our theme allows us to insert codes directly into the header while some themes do not. You may need a plugin for header scripts.