Not bad. You should post this in the Pixel Art section ( or request a mod move it there ). Looks like you have some regular graphic art experience.
Generally on this forum it is encouraged that you use only as many colors as you absolutely need. For me this is usually around 20 colors, though it could be more if it's a picture with many different elements.
This picture could easily be reduced down to less then 20 colors. I'm sure some people could get it down to 10 or less.
Here is an edit using just 5 colors, my guess is 3-4 more colors could finish it.
