From your FLA file, there are a few things to do to speed up your code.
No alpha tweens on vector images. This is a huge performance hit. Try changing the brightness value instead, or even finding a way to skip the tweens entirely.
You have a lot of vector images that don't change. cacheAsBitmap will not necessarily help the loading time, since the bitmaps are generated at runtime. Since they are essentially bitmaps already, just make them into bitmaps. Figure out the largest size you will need, export them as an image, and then import them into your library. Then just swap the vector image with the bitmap image on the instance's property panel.
Reduce the number of active tweens that happen at startup, if possible.
Get rid of the transparency on the clouds. Make the background match the background color.
If something is not moving at all, like the hills, merge it into the background, if possible.
All told, I would have 3 layers: background, foreground and moving middle ground. If this animation will never be made into fullscreen, I would merge all the individual fruit, leaves, etc. into the tree, and create one bitmap out of it . . . or two, if there will be a foreground layer.