Scene Change Delete Current!

Godot Version

4.2.1

Question

On new scene loading should I delete current scene before loading next scene or godot automatically deletes current scene by itself?
I have two scenes. menu and level 1. If I play any scene, menu or level 1, by pressing play current scene button, the scenes runs without any fps drop. But if I change the scene from menu to level 1 by code fps drops below 15.
I just followed a youtube video to make the loading screen. The link is here - Loading Screens in Godot 4.