There are already a few posts in this forum on optimisation. Have a search to find them.
As for object culling, here’s a post on it that may be of help.
As for event optimisation, consider using a FSM (Finite State Machine) to control what events are processed. So instead of GDevelop running through all events, a FSM will section off and run through events that are specific for the games current state. You could probably do the same for object/players, and depending on what they’re doing, only have events for each state.
On the whole, eEffects tend to be a processor hog. Not sure how to improve them without removing them.