Number of Sprite Atlases may terribly slow down loading speed

I don't know if it's a known issue, or only happen on my computer, but it sames like that loading speed would affect by the number of atlases, which means the more sprite atlases exist in my program, the slower the loading speed of any prefab dependencies those atlases, no matter if those atlases are used by that prefab or they just exist in program.

Got about 400 textures in this program, packing them into about 50 atlases by setting difference Packing tag.
There is a simple test as follow:
Load a prefab that use about 4 of them:


Remove Packing tag of most of those atlases, left only 1 atlas exist:


Please keep in mind that the only difference between them is, I removed 49 Packing tag before the 2nd test.
And in my real game, there are far more than 50 atlases exist, thus made loading speed unacceptably slow.

I'll try to upload the test project.

 

I've upload test project at https://github.com/tanghuipang/testLoadProj

//Anybody could tell me if I post this thread in a wrong place?

 

Why there is nobody even care about it? This is serious!
By the way, I've report a bug to unity about this, and then after one day they close it without any explain.
Anybody who saw this thread, please at least try it, let me know if what I say is true.