Here are my steps to getting down to 115 on a 5'9 frame:
1. Jam finger down throat.
I'm going to be honest, I don't really think that being a model is worth being an unhealthy bag of skin and bones with no muscle mass. I'm sorry, but primal advocates being lean and strong, not being scrawny enough to escape between two jail bars.
If you want to get down that much, I don't think primal is going to be very helpful. The only way I could imagine getting down that low is by starving yourself, which I am sure you do not wish to do.
Remember, you are unique just like everybody else.