What is best and optimized Technique of level Handling in Parking game ? loading from resources or enable in hierarchy

I am developing a parking game in which i have 50 levels. The outer environment including buildings and floor is similar in all levels. I have created levels prefabs with different props like cones, cars, boxes and arrows. i am instantiating these prefabs from resources . I am searching for which is best approach to handle levels i.e. 1) all levels present in hierarchy and are disabled and only current level prefab is enabled in start or 2) i have to instantiate each level from resources when level is selected. I am working only in one scene.