This not true, Nativization only improve performance if you have complex Blueprint setup, but never be 2x.
With regard to performance issue, there is many reason, have you checked shader complexity ? , maybe you are using expesive materials, I once able to save 10 frames on my phone just by changing my material from additive to masked for particle materials . if you have no logic or actual game play , i’m pretty sure its your shaders
Check out this