Las que empiezan a los quince años (1978): The Beginning [of TeenProstitution] at Age 15 [in Spain]

As there doesn't appear to be any subtitles and despite the fact that I live in New York, I was able to understand very little of Spain's Las que empiezan a los quince años (1978) [English: The Beginning at Age 15]; therefore, let's rely on Andrabem's IMDB post:

"Las que empiezan a los quince años" tells the story of the sexual adventures of three fifteen-year-old girls: Elisa, Marian and Susi.

Elisa lives with her father and her stepmother. Her father, drown in debts by reason of bad business decisions, has to run away from his debtors. Elisa remains with her stepmother that has no love left for her. Soon Elisa is out in the streets. One of the roads left for her is [teen] prostitution. Her life will be one of many adventures and misadventures.

Marian, very early in her life, became a prostitute. She had known a good-looking [much older] guy in a party. She falls in love with him, but in reality he's a pimp. One day they have a fight and Marian decides to become independent. She opens the doors of the cars and ask the drivers if they want some company. On seeing this beautiful Lolita, many say that, yes, they could do with a bit of company.

Susi's family has no financial problems. Her father works a lot and is always absent, but her mother likes and understands her. Susi likes girls. She sometimes plays innocent little [nymphet lesbian] games with Elisa and Marian.

The film offers a rosy vision of [teen] prostitution, but anyway it had no intention at all of being a documentary. The film wants to titillate, and it delivers. The [teen] girls frequently take off their clothes, make love, laugh...

I'll add that Elisa (Sonia Blanca), unlike Marian, isn't drawn to prostitution. Consequently, Elisa, to the chagrin of her stepmother, (eventually) rebuffs the advances of a middle-aged john. However, Elisa is attracted to older men. For example, she goes home with a seemingly wealthy man whom treats her like an adult by giving her a drink and a smoke, but instead of charming the nymphet, he drugs and rapes Elisa. In addition, Elisa is raped by a businessman after he witnesses her seductively cleaning at the office. However, in the end, Elisa does have, at least, one consensual age-gap love affair.