What's it like at communiy college?

IN the US
Everyone class schedule is different.
If you have 15 credits for the semester you will be in class 15 hours per week. Rule of thumb is 2/3 hours of study time per credit hour. So you will have 30/45 hours of study time per week.
Most classes are worth 3/4 credits. Classes usually meet for one hour M/W/F. Or for 90 minutes T/Th.

Some freshman classes are be huge- 100 students in a large lecture room. Smaller classes usually require class participation.

You'll be in a class where most of the people are there to learn. Most students have plans for their lives. Classes last 1 to 3 hours, but you study on your own time. Study groups are encouraged.

It depends on the classes you take. You will be switching from classroom to classroom. You will be held to a higher standard of responsibility for your assignments and study. Your grades go on official college transcripts and course credits usually transfer to other colleges.

The majority of the people there will be older than you as most will have either graduated high school or are pursuing continuing education.

Think of it as studying in high school without the distractions of popularity politics, puberty or zits.

I teach at a community college and have never heard of 100 students in a lecture room (except at universities). The idea of CC is to start students out on the right foot for their academic careers. Fifteen credits is full time. Each credit of class equals an hour or class time per week, plus you will need to read, study, write, and work on projects. Unlike HS, your classes may not be every day and may not be right in a row. You could have one class that meets 2.5 hours on Tuesday and Friday mornings, one class that meets 2.5 hours on Tuesday and Thursday evenings, and one class that meets M, W, T or an hour and twenty minutes. When you meet with your advisor, try to schedule times that are most convenient for you.
If you do have time between classes, make the most of your on-campus time: study, go to the tutoring center, work out in the gym, join a club.
No one will know you are 15, unless you tell them. In my state we have a program called Running Start, so we have many high school juniors and seniors on campus. Some are more successful with the transition to college than others.
I think the biggest difference between HS and college is that now it really counts. If you mess up your GPA, it is messed up. At the beginning of each course the instructor will give you a syllabus that outlines the course expectations, schedule, and due dates. Read it and pay attention. Late assignments and second chances are rarely given. The other big difference is that people are paying for their classes and books. Even if you are in a program that pays your tuition, the bulk of your classmates will be paying, so generally people who pay take their education seriously.
You have a great opportunity: enjoy it and learn everything you can!

Graduate from high school first kiddo. Unless you are a prodigy, you are not going to go to community college. Most community colleges are commuter schools, so mommy or daddy will have to pick you up from class.