Thank you so much for the reply Camille.
I had gone through all the links you have provided and I try following the optimization tips as much as possible when creating the textures. I have even tried changing the settings for the load behavior to all options provided. After changing I did a build & run again, but it does take the same amount of time and I saw no change at all even with "do nothing and cache," option it still gave me a long loading time and there were no textures generated.
Currently I am using substance file downloaded from Substance Share.
In case it helps here is a dropbox link with the Unity Package (v5.3) and the build too - the archive extracts to 457MB
https://www.dropbox.com/s/p6ggc2tpdjp32w8/test_level.rar?dl=0Wonder if I am missing anything here? Especially while testing the loading with simple sphere with substance file and using build and run from Unity.
Regards
-G