Script? 
Doesn’t this mean the script ISN’T 17 MBs?
Are you referring to ??? when you say script?
Because I thought that meant the game engine.
In my (admittedly limited) experience, the scripts for these games are ususally written in a scripting language designed for visual novels. You will have a command that says “character [$1] says [block of text]”, another command to change the music or play voice clips, and so on. What people normally would call a script - a text dump of all the text the game displays in the textbox - is usually not stored separately from the scripting language commands.
I would guess the 17 megabyte figure refers to the ‘script’ in that sense - essentially a program containing the ‘game script’ embedded within it - and not “there are 17 megabytes worth of text displayed by the game”.
Yeah, I normally call the script the scenario is programmed with ‘the script’ and the text in it ‘the text’, so when I say an eroge has 4mb of text it’s just the text I’m talking about.