I had the same question, thanks for posting it. BTW, You have to wait 1 year not 2 before applying. Personally, I figured I'd be Y-4 as Y-3 is minus 3 maximum I am minus 4.5. You only need Y-3 to join Paras. If you do not want to join Paras the whole surgery thing is pointless really. However, there are other things to keep in mind. How good is your French? Mine was really good until I was 18 (23 now) when I joined an English department boom no French no more and I forgot everything. What I want to say is that you may want to consider performing the surgery (if you can afford it) then wait 1 year and during that year you would work on your French. From what I have gathered here, French allows you to get promoted faster, gives more prestige and of course will help a lot in a naturalization process I think no matter how good as a legionnaire if you are not fluent in French I don't think you will ever get a French citizenship even if you are Rambo. Otherwise, you go there ASAP and learn French there. You may have a better learning experience in your country. I read negative comments on the internet on the way they teach French in the legion but that may be some false propaganda maybe an actual service member can help us in that. Other stuff also to keep in mind is how expensive is eye surgery in Mexico? Here (Egypt) a PRK which is usually prefered by military institutions goes for a maximum of 4000 EGP which is well like 300-400 Dollars it is very cheap in my country. Can you afford it in Mexico+ visa expenses+ air ticket? Keep in mind that in your country it might go for as high as 2000$ like the USA, in France I think 2K+ euros You have to think about that. 300-400$ are pretty affordable for anyone a round air ticket will cost me the same, so it is easy for me to do it here. Also, did you check whether you are eligible to be performed on or not?
Sorry for the long talk, you have the same issue as me so I thought I'd share my problems with you because they are probably the same problems you are facing.