This was a decision I had to make 30 years ago for myself. I attended a very rural, small public high school. Out of a class of 80 students about four or five would take Physics and Calculus as seniors. The same teacher taught both classes, and was very clear that he didn’t really understand the subjects that well himself. All of the social studies teachers, and most of the teachers of all freshman and sophomore classes, were coaches. I was miserable and dying intellectually, and knew I had to make a change.
It sounds like your situation is not as dire as mine was, but I can tell you some of the benefits I got from my STEM boarding school that I would not have had at a regular public high school, even one that was better than the one I attended.
I was exposed to a much wider variety of people (ethnicities, religions, orientations, backgrounds, everything) than I could have been otherwise.
I was challenged to my limits, but had an extreme amount of support that allowed me to meet that challenge. We took 7 to 9 classes each semester, and most of them were college level classes. However, we had absolutely the best teachers and very structured support, that allowed me to develop good learning habits and good study habits, as well as learning the material itself well. It was such a good preparation that when I went to MIT as an undergrad, I found it very easy. I graduated with one B and I never felt stressed out or anxious the entire time I was there.
The school knew of opportunities for enrichment and research that I would have never known about, and I think even most high schools in the state did not know about. Also, they had very good connections that helped their students get into those programs. I went to Japan for a few weeks after my junior year as part of one of those programs, and I spent the rest of that summer doing research at a well known (but not T50 ) university as part of a residential research program for high achieving high school students.
Even if I had been at a better high school than I was at, I would not have known which colleges I should apply to, and how to get in. The STEM high school had amazing college guidance counseling resources. They told me to apply to three schools, I got into two of them with full rides and the other one was MIT.
I also was not sure I wanted to do STEM, but the background and the skills I got from the school for worth it for me. Additionally, the teaching was so amazing that I would prefer to be taught chemistry (my least favorite subject) there over sociology (a field that I found out later I really enjoy) almost anywhere else.
I am not saying that you should choose the STEM boarding school. But I did want to help you see some of the advantages you would have with a program like I attended, that you will not get through doing dual enrollment at your current school.
As someone else said, it’s definitely a significant lifestyle change. I knew very intelligent kids who ended up dropping out in the first year because they just did not like living away from home, or giving up some of their social opportunities or sports.
ETA: my boarding school was a state sponsored school, so I paid nothing for it. If you are talking about a school where you are paying tuition, especially if it’s college price tuition, that’s definitely a consideration!