low-end pc

i wanna know if i could lower resolution like in textures and terrains only when i'm edditing but when i want to build my game iwill get everything to how it was

Texture Quality can be adjusted in the Quality Settings menu.

You can create a lower quality level option for use in the editor and don't make it available for the player in your game's own options menu. I can't confirm if the Texture Quality setting affects the scene view in the editor, as I haven't specifically tested that, though other settings in there I know do affect the scene view.