What browser are you using? The default 'android browser'? Also, you may have an older android phone? Some more details would add some context to your post.

What browser are you using? The default 'android browser'? Also, you may have an older android phone? Some more details would add some context to your post. They also have a way to wrap the JS app as a native app similar to Cordova. The games I've tried on my Nexus 5 worked fine with a great user experience.