Rendering a screen sized object per tick will always impact performance, even when the smallest possible source is used. It's the size of the screen that is a factor here. If your game runs at 320x240 full size objects will be rendered faster then at 1920x1080.
If you experience just some minimal performance impact when previewing, but a drop to half via CocoonJS, chances are that there's some bottleneck in CoccoonJS.