Rendering in background is too slow.

Hi everyone.
I’m trying to automate rendering process of multiple files by using “.bat” commands like these:
“C:/Program Files/Blender/Blender.exe” -b “C:/Project/Scene1/1.blend” -o //1/render# -f 1
“C:/Program Files/Blender/Blender.exe” -b “C:/Project/Scene2/2.blend” -o //1/render# -f 1

And so on. The problem is that this rendering process is waay too slow (6-8 times) than rendering normal way. I thought it should be at least the same (no UI etc.). What am I doing wrong?