30 second delay when running the build

Hello
So I’m testing out instantiating terrains with mesh grass applied. For this test had a 500x500 terrain with 200000 mesh tree grass.Scene has only a light, plane ,empty GO to act as trigger and the standard fps controller…Terrain is made a prefab and placed in resource folder…But when I press play in the build it takes 30 seconds or so before can even move then I run a few steps and hit the trigger to instantiate the terrain which works fine with only a slight drop in fps. But why is it taking so long for the build to start from pressing play.When i run it again then it start instantly.Tried as development build and profiler attached but the profiler never recognises the build.

Well finally figured out how to use asset bundles but makes no difference the delay in the build startup is exactly the same as with the resources.I’m confused arn’t things in resources folder and asset bundles unknown to the build until they are actually called via script so why is there such a massive freeze at startup on a very simple scene.I know that if I run a scene without any reference or inclusion of the terrain in question it takes 7 seconds for the build to unfreeze so what is up here?