The S3 mini is an antique, in HTML5 terms.. Getting anything to run reasonably well on a device like that is quite a task. Even without physics and effects you have to be really careful and optimize aggressively, to get things done.
Try the following: New project, set the resolution to 320*480 (portrait), set full screen scaling to low quality (very important!) and put a few sprites onscreen (a few as in: 5) and move them a bit and then check the fps.
If you need your games to run on devices like that you are pretty much restricted to a few genres, that do not require too many and/or too large objects, and preferably don't do any scrolling. If you read the guides already, you might want to look again at the sections mentioning overdraw. On "crap" devices like that it really helps performance to minimize it.