Time Limit for Entire Project

Hi! I've built a software simulation. Part of the simulation tests that the user knows where to click given an instruction, and the other part of the simulation presents true/false or multiple choice questions to the user. It's a blend of both of these parts.

Here's my question: How do I add a "universal" time limit to the entire project? I don't want the user to spend more than 15 minutes in total to get through all scenes/slides/layers. I'm hoping there's just a setting that I'm overlooking. I thought maybe this would be possible if I use a single slide and have a million layers, but I don't want to do that. The course is essentially complete, and there are 6 scenes, each with up to 3 dozen slides, some slides with up to 7 layers.

Thanks for any help!