first Launch on mobile takes hours?

It’s my first mobile game, so after setting up all the USB-stuff, i finally launched the game on my phone. I use only etc1 texture compression, but it freezes the engine completely for ~10 minutes, some shader processes in the background, and after that it is now “Processing Assets for Android” and compiles 9000 shaders, which will take very long. (I just export one simple level with only 50 unlit actors, my content folder is like 30mb maximum with like 5 materials, so i have no idea why this takes so long)

My questions: Will the next time i hit the “launch on device” button freeze my computer again, and will all those shaders be recompiled again, or is it just a one-time-have-to-go-through-thing?

Since 9000 shaders are compiling, is this normal? I think normally would be like max 3000 shaders to compile the whole engine default stuff, so even if i have unchecked all except etc1 compression, it is compiling shaders for all those compression formats now?

Thanks for help.