Use smaller images at a lower quality level, use fewer frames. But a gif is not capable of substituting for a movie. An average size for a animated gif would be less than 100KB, way less. You can't make a short movie clip work as a gif. Two frames maybe, like a before/after kind of thing, but much over that, you're really pushing it way beyond what it's meant to do. There's a reason the animated gifs you see on websites are mostly pretty tiny.
