Performance issue when previewing from scene/layout editor screen

This is actually have been an issue for long but I just remember to post it now. I have performance issue which the game is lagging/feels heavy when previewing from the scene/layout editor screen. I do have a low end pc but, when previewing from event editor the game run smooth. So, everytime i want to preview i need to switch tab to event sheet first before hitting the preview button. What probably causing the problem?

When the preview is run from the external layout editor, the software loads the scene, then loads the objects from the external layout, so the objects are in double.
This has been reported and may have been fixed recently, I haven’t checked.
Either way, you’ll see if that’s your issue by opening the debugger and checking the number of instances.