You can use the QuickTime screen recording and the iOS Simulators to do your video recordings. The tricky thing here is to get the correct size so that iMovie can detect the output resolution when you go to export the AppPreview. I haven't found a way to select the output res in iMovie so if must detected by the format of the media you are using. It may take you several tries but it's doable. It's one of those: do I have $300 for FinalCut Pro or do I have an hour or so of my time? You only need three recordings as mentioned above. I could actually do two of them on devices because I have them but I don't have an iPhone 6 (yet ... :) ). I also like the simulators because you can use something like SimFinger to simulate gestures and pressing of buttons.
Good luck!