@WindyWaffles basically this, although depending on how many actors you have, you might have to refresh the status window many times, and since the draw_text is called withing refresh_status, it might cause lag. That said, I can hardly see how enough actors to cause your game to lag can be on the screen at the same time unless you completely changed the battle GUI... And if that is the case, you problem is more likely to be caused by a poor memory handling in the GUI script rather than being related to the draw_text method.
In short, while the draw_text method might cause the game to lag, it can only do that with a script that completely changes the GUI, and if you have a script that changes the GUI, I doubt the draw_text method is at fault.