Just for some context: Every event box is processed in full, every frame, from top to bottom. Their actions occur, then then their subevents process in the same way (if the parent evaluates true), then their actions, etc.
Your first event will process all of the conditions, even if the first condition is false, because it’s part of the same event box. The final result of the event conditions will be false because the first condition is false, but it still has to go through the full event condition set. Edit: Even if you ignore the “Or/And” logic needing to be processed, it still means it has to build out a list of potential objects to evaluate every time, which is definitely going to take up processing time.
Your second event will only process the subevent if the first event is true. Less to process, therefore it runs faster, and is generally the right way to optimize your events.