You have several options here. You can try theDetect and Track Multiple Faces example on the File Exchange, which detects and tracks multiple faces. You can try the same thing: replacingvision.CascadeObjectDetector withvision.PeopleDetector.
Alternatively, if your camera is stationary, you can usevision.ForegroundDetector to detect any moving objects. SeeMotion-Based Multiple Object Tracking example in the Computer Vision System Toolbox.
In either case, if you want to track people reliably for 10-15 minutes, you will have to do a lot of tweaking and tuning of parameters.