Is it possible to delete parts of the course in the middle of the timeline?

Hello! I built a course but now I do see that I would need to remove about 15 sec in the middle of the course. And move all my items  about 15 sec to the ledt in the timeline. I guess there is an easy way of doing that...that I just cant figure out! I would be glad if  you  can help me out! Thank you in advance//Tanja