After the advent of the censorship filtering system, age ratings were adopted around the world. Now porn or violence is designated as 18+, in some countries 21+. The law you are referring to says the limit is 15 years, this is included in the 13+ category. Where did you find in the law that children can watch 18+ or 21+ material?
If you've read the bloody thing through it says:
"
§ 6 At a public gathering or a public event where a presentation of a film is shown, access may not be granted to anyone who has not reached the minimum age determined by the authority in accordance with § 5, unless otherwise follows from the second paragraph.Children under the age of seven who are accompanied by a person over the age of eighteen may be admitted to viewing a presentation that is permitted for children from the age of seven. Children who have reached the age of seven but not eleven and who are accompanied by a person who has reached the age of eighteen may be allowed access to the viewing of a presentation that is permitted for children from the age of eleven. Children who have turned eleven but not fifteen years of age and who are in the company of a person who has turned eighteen may be allowed access to the viewing of a presentation that is permitted for children from fifteen years of age.The government or the authority designated by the government may issue regulations on age limit grants.
Law (2017:78).
§ 7 Notwithstanding §§ 3 and 6, anyone who has turned fifteen years of age may bring children who have not yet turned one year old to a screening that has been specially adapted for parents who bring infants with them."
You're totally ignorant to the text!
It's in plain sight that the person aged 15 is at the top of the ladder.
This is the law that define and regulate at what age you're allowed to watch films shown at a public gathering.
3 limits: 7, 11 and 15!
A swedish 15 year old is considered an adult in this respect!
Do you in the law text, that I provided in full in both languages, find any restriction of 18 or 21?
18 is only applicable, as I mentioned before, about alcohol, voting and driving a car!
21 disappeared over half a century ago.
18+ or 21+ does not apply in a cinema in Sweden.
Different countries have different rules and regulations.
In plain italian: Basta!