I don't do the course, but I have a few friends that do it and a few that did it last year. At our school the major work was something like 2600 words so not a whole lot. I'm not sure if it's the same at your school but at mine there is a fair bit of class time to work on it. Most of the people I know who did ext. history spent most of the year researching then about the last 2 months of the course writing/editing it.
I think Ext. history and Ext. 2 english have a lot of freedom in the course and not much guidance so in turn, less organisation which can be a bit scary. I dropped Ext. 2 english because i didnt want to do the major work and also found it a little too disorganised.
If you enjoy the content you did and are excited about your major work, I'd recommend keeping it as that will help you do well in the course.