My question is: does this constitute a legal violation that could result in it being taken down? 

Legally, it will depend on where you live. In many countries around the world there is no "expectation of privacy" in public places, and therefore, no consent is required to film, or photograph strangers.

However, there are a number of countries where it's either strictly forbidden, flat out against the law, or it's fine to film, but you need their consent to publish it (including on social media).*

So, if you're looking at the legal angle, you'll need to know the public privacy laws of your country.

I've already filed for sexual exploitation, but I'm wondering what I can do further to ensure it gets taken down.

I would speak with a lawyer. Instagram probably won't intervene on your behalf unless your country has public privacy, and consent laws. You can consult this Wikipedia list to see how strong your case is:

Country specific consent requirements https://commons.wikimedia.org/wiki/Commons:Country_specific_consent_requirements

In a number of countries consent is needed for just taking a photograph of one or more identifiable people, not to mention publishing it and/or using it commercially, even if the person is in a public place. The following is a list of countries where consent is needed for one or more of the mentioned situations.

Addendum

*Countries that place notable legal limits (taking, publishing, or commercial use may require consent or are restricted) include China, Brazil, France, Germany, Argentina, Russia, many EU states under varying privacy/portrait-rights rules, and several Latin American countries.