Any content should always be in a container. The 15px margin keeps the content from laying against the side of the browser. If you want to do a fullscreen background or image or something then you don't need the container.
If you need multiple bleeds on a page, use multiple containers. Just don't nest containers inside of containers.
For images that you want to touch the side or whatever, there is some of that fiddling with the margins on the interior elements, yeah.