avoid every tick event (every tick, is on layer , is visible etc ...)
enable collisions only when it is necessaire
optimize your all your sprite size
set web gl to on
set clear background to no
try to read performance and optimisation tutorial on forum
if still same , you have to post . capx to see what go wrong
i believe that construct 2 can do fantastic game with nice effect ... just take look too scierra game but we have to learn more and more about different features AND every one his own logic .... an action can be made by different way ... it depend of every person logic