Reniaa,
You are correct, it is personal choice, until you are told by some elders you will lose your privileges.
Generally in the United States, witnesses do not watch anything rated "R" - there are some who won't even watch PG movies.
There are those who would enforce a choice on some - you watch this and I won't hang out with you.
In the UK the "15" rating would probably be considered "R" here.
I believe Bethel has one of its questions as "do you watch R rated movies", so even though they don't have a list, the implied list would be quite lengthy.
The Bible does speak about Jehovah hating those who love violence.
At the end of the day, if you rent an R rated movie which informs you that it "contains graphic violence, sex and scenes of drug abuse" you have been warned, but it is still personal choice.