Is it possible to make a textbox advance faster?

No. Textboxes already display very quickly (all the text is up in roughly a second), and there is no way to make them faster.

If you want to create textboxes with special advancements effects such as pauses, variable speeds and scrolling, such as those in FF6, you can fake them with scripting and strings. However plotscripting every textbox you want treated this way is labourious, and won't be described in this article.