I guess there are many of us has problem with performance issues. I try to make a sling shot game as you can see on links below.
I will try to explain them as shot as possible. Game is using physics but there are only 3 objects with physics and 2 as plain sprites.:
1- Graphics glitches on laptop while playing. You can see how the circular sprite look like on the image below. (It's just on right of the play icon). It's not happening all the times but most of the time it is like that. Funny part is debug mode show max 2mb memory usage and 59-60fps all the time.
2- On mobile.. Well. It's just painful to watch the ball in most probably 1fps. I can't understand it, simply can't! I may not have the highest end phone or laptop and also C2 HTML5's may not be as fast as a regularly coded native stuff but.. This shouldn't be like this right? I read those Performance Tips but i really don't believe my problem is written there because i don't have any issue mentioned on those articles.
Can you just try the game on your mobile and pc and tell me how are they look? (If you press 'R' on both by touching or from 'R' key on keyboard game will restart itself.