Look like you posted your topic in the wrong place, go to " How do i" section: https://www.scirra.com/forum/how-do-i_forum45.html
But first i want to ask you, what kind of game you make ?? (platform, rpg, puzzle etc...??)
If you use physic, the R129 released support native box2d in cocoonjs, upgrade to r129 and try your game again, the performance with physic will increase with great result.
Feel free to email me:
I have a lot of experience about performance.