Im pretty sure even dough you got a good point, they will not allow you to play it.
Im 16, i have played allot of violent games and my dad have approved on all of them ( Witcher 3, Skyrim, Call of Duty Modern warfare and Ghost, Battlefield 1, Dragon age, Wolfenstein 1 and 2 aaaand shadow of war and Mordor), but if i would ask my dad to play Gta he would never say yes, beacuse him like most other adults think
GTA games makes kids wna commit crimes like fighting, killing, stealing, street racing, heists. Maybe try to convince them that you dont wna commit crimes and that you are a good kid or something
Seems to me parents don't dislike gta over the violence but the criminality and such, so Just cause and fallout are not something they would compare GTA with.
I played GTA 5 allot anyways (100-200 hours) and he never noticed, i was just carefull when i played it and tried to cover the screen or make it look like i was playing something much less violent like a racing game. Maybe you wna just try to play it behind her back? If you do that, make sure to try to only play when home alone if u are afreid to get caught