I never used Construct Classic, so I can't really comment on that - but as elisamuelps already pointed out simply by running the numbers, switching your effects to simple particle systems or animated sprites sounds like a good easy win.
If your effects are causing the slow-downs, you need to find a way to re-create a similar effect more efficiently. This usually means less naive resource handling, less objects, less object creation/destruction, more sharing between objects, etc.