I libe in mexico city and my cookies tend to come out really flat, I'm scared of using the two sticks of butter, how much can I leave out before i...

The author seems from the notes to have intended for the cookies to run- the fat/flour proportion is a little skewed toward fat, but not by much. Any change at all in this proportion will affect the texture, but not necessarily for the worse.

I'm not sure, from your post, if you are asking two questions or two parts of a larger question.
E.g.,
1a) you don't want to use two sticks of butter (for fat, calories, whatever reason)
1b) you don't want to use (waste) two sticks of butter and again have your cookies come out flat.
Which leads to question 2, why did your cookies come out flat.
Agree with E's answer about problems coming from messing with the rat/sugar/flour ratio in baking.
Glad, also, that you told us you live in Mexico City because (perhaps) altitude (7382 feet or 2250 meters) is a factor here.
Do you adjust your baking for altitude?
If yes, I have no more suggestions.
But if you do not already make those adjustments, have a look at this article (and maybe others you can find yoursef) for useful suggestions:
http://dish.allrecipes.com/high-altitude-cake-baking/

I find that with baking, changing the fat:sugar:flour ratios asks for trouble, but maybe someone else will know how to reduce the butter content... Maybe if you don't want as much butter per serving, you can make smaller cookies and adjust the bake times accordingly so it feels like you're eating less fat?