Well, I'm not sure what you mean by a "skit" but as soon as you author something, you immediately have the copyright to it. You do get some benefits to obtaining federal registration of that copyright, but I guess the question is, what, exactly, do you plan to do with this 15 second "skit". How will you exploit it? If you're going commercial with it, then it might be worth it. If not, if this is just a goof thing for you and your friends, then I'm not sure that it is. Getting a copyright registration isn't all that expensive, though.
It depends on how much commercial and legal protection you want to get from it so that you can exploit it economically, and how vigorously you are willing to exercise that protection in case thre is an infringer.
