Mur, please do not take this as an insult to your work. I think it is pretty good but requires a little more effort on the palette control aspect. And I am not the only one to decide which work goes into the gallery or not. We try to evaluate pixel works as a team.
You don't really have to remove anything.
There are lots of colors in your palette that are almost identical but just a little different in hue, saturation or value.
Please follow this link which shows the color information of your work:
http://yanrishatum.ru/pj/?input=http%3A%2F%2Fpixeljoint.com%2Fpixelart%2F123553.htm%23c589091
Move your mouse cursor over the colors towards the very end (scroll down the palette) and you will see which color is used where.
Try to group similar colors together, this way you will reduce color count greatly. If you think you can not group any similar colors together that's ok too, cheers.
Do you see the picture in the frame?
Do you see dirt in the plate?
So what kind of overkill are we talking about?
Well, I will remove the picture, remove the plate, the meaning of the game is lost, but then there will be 64 colors as you want! Wow!
This one has 256 colors, that's overkill. You have lots of single color pixels lying around.
You should try to clean this up a bit.
Theme Hospital from Bullfrog :)))