Yes don't do it your self, your going to leave a ton of bubbles and maybe even wrinkles. If the legal limit is 70% I would just say screw it and go for some real tints.

 

I don't get why you would want to even go darker than 15%. That's pretty dang dark! I have 35% all around and it's dark enough at night time. My brother put 20% on his Charger R/T and I think it's too dark. It looks nice, but you can't see jack out of it at night.