The biggest problem with Android performance is GPU blacklisting - the drivers are buggy or unstable and so the browsers revert to software rendering, which can really tank performance. The best way to check for that is open Chrome and visit chrome://gpu and see what the status at the top is. WebGL should say it's hardware accelerated in green. If WebGL and canvas2d both say software rendered, you probably can't get good performance on that device. (Most modern devices are fine though, this is typically only older phones)
If both are hardware accelerated, then you simply must make measurements otherwise you are shooting in the dark. If the CPU usage is high, try running C2's profiler in debug mode and it will tell you roughly where your CPU usage is going. If the CPU usage is low but it's still slow, the graphics are too intense.