I may be a little late in replying to this post, but here are my thoughts. I don't do a lot of video editing, but many years ago I used to work for a company that supplied the equipment, back when digital video editing was first coming out.
I would recommend you first learn cut only editing with adding beginning and ending titles. This means taking the 15 minutes of video you shot down to 3 minutes of relevant content someone will actually watch without getting board. Add a title for 3-5 seconds at the beginning and information on how to find you at the end. This can actually be done fairly well with the free YouTube editor, assuming that is your intended destination for your videos. My personal experience is I spend most of my editing time cutting out stuff that is not needed.
What the YouTube editor does not have (at least that I could find) was a way to speed up the video. Sometimes when you are filming a longer process you want to run at 4, 8 or 16 times speed so you don't bore your viewers. Therefore I'm back to using the Windows Live Movie Maker that is free to Windows users. I'm sure that iMovie for the Mac is similarly capable. I believe you will find that until you are much further along in your video editing endeavor that this software will do almost, if not everything, you need it to do. I used to have access to a couple of mid-range video editing packages and it was so hard to do the simple cut only editing that I needed I ended up going back to Windows Live Movie Maker. If you remember the 80's & 90's everyone wanted fancy complex transitions from one video to another where a video flys in on a ball or spaceship and takes over the screen. However people have moved away from that as users don't really care for it, they find it distracting at best and annoying or un-watchable at worst. When moving beyond cut only editing to a transition you really only need some basic fades, wipes or dissolves which I believe these software packages do.
My recommendation is unless you know that the basic video editing software that is free with Windows or Mac will not do what you need, then start with these free options. Note that they usually are not pre-installed so you have to download and install them, but again they are free. Of course if you are Linux desktop user this advice doesn't help you much