Amazing colors and likeness! splendid job done

1.Concept art is more of a solution to a design problem like a proof of concept that uses art to convey to the game devs that this is how a certain object in the game would function and it has to be designed in such a way. You are laying out different view angles and cross section of something that needs simplification. Whereas illustration is your book covers, trading card artwork, comics. 2. No not at all, your portfolio will speak for you. Just don't mix up too many different genre and styles of artwork in your portfolio. 10-15 best works and cater them to the studio you apply to. 3. You are 15! Hold your horses a little. Job comes later. But won't discourage you from working on building a fanbase. Work one step at a time. Chose one direction and improve in that aspect of art first. Art school is too expensive, online workshops and mentorships are better as you can opt for monthly payments. Right out of school you could look at joining event management companies to get exposure to hosting and arranging event like comic con and other conventions. There you will meet many like minded people and you would gain clarity where you want to go. Since you want to work at xbox, you can learn a programming language and get into the game industry as a programmer. For where to apply for jobs, you should check out artstation jobs, creativeheads.net, and 80.lv has curated jobs for paid members. I hope I was able to answer some of your questions. Keep creating!