Chaas98,
Welcome! FYI, when you signed up here and asked your question, you probably took a bigger step closer to playing baseball in college than if you’d increase your average by 50 points. The reason I say that is, in order to play college baseball, you got to be in college and get good enough grades to be eligible. That takes a level of mental maturity not a great many 15YOs have. 
Now that you’re here and have asked your question, hopefully you’ll get lots of answers. Read them all and be sure to give them some thought, then weigh their value.
I’m gonna take what isn’t a very popular tack, but try to understand what I’m saying. Assuming you have the grades to get into college, in my experience, if you’re a starter on your HS varsity team, you’re good enough to play college baseball somewhere.
Before you get the wrong idea about that, you need to understand that just like HS, in college there are many many colleges, and many many different levels of play, and you have to consider things that way. There’s a difference if you’re barely starting in right field as a Sr for a very small school who doesn’t play many quality teams, and being a 4 year starting SS or pitcher for a HS with a very strong baseball program with a lot of competition just to make the roster.
Hope you noticed that I didn’t once talk about specific numbers, and the reason is, the numbers are different depending on the situation. If you want some idea about what what a “good” average is, go to http://www.maxpreps.com/list/s...rsport=boys,baseball and look around at the averages for each category. The higher on those lists you get, the more opportunities will open up for you.
Good luck!