Use this cheat to make the balls slower:
Go to the "\levels\folder" and find there a file called "levels.xml". Make a backup of this file to avoid some unpleasant results and only then open it in your text editor. Search for the line which contains this:
Settings id="lvl11" speed="0.5" start="35" score="1000"
Here, "lvlll" means Level 1-1, so you can find any line corresponding to the needed level and change the speed to 0.2. Now, when the parameter is changed, save the file and enjoy the effect!