is it absolutely necessary to put 'Esenthel script' on the startup?
I would rather it be put into credits page instead.

Is there a way not to advertise this?

You're using a commercial game engine for (nearly )free.

Yes, it is necessary to put it on.
Is it a big deal? It's a splash screen of 2/3 seconds.

You need to show Nvidia logo as well.(worth mentioning)