I don’t know much about the better ways to enhance performances on html5 platform (and android builds), but i think that maybe you shoud try to take a look on other subjects about assets and code optimizations :
[url]Appropriate size and dimensions for a web game - #9 by MeX1Co] (in short : images => tinypng)
[url]Optimization Tip Compilation: Post Your Tips - #5 by Kink] (in short : mixing several optimization for the native platform).
Maybe try to use the less possible number of chronometers (or refresh values by “step”, instead of each millisecond), add “do once” everywhere it’s possible in events, reduce size of images/animations (better keyframe/less images)… I guess these tips works on every game engine.