Quote: "Yeah, but when it's low-poly, the texture make everything of the model. "
I know what you mean, it is hard to sacrifice detail from the geometry when you have something you like and looks good. But, at nearly 18000 people aren't going to be able to use the model, it is just too high, the lead supporting character in Half-Life 2 (Alyx) only had 8323.
Here are some easy ways to reduce the poly count on your model without any loss of detail.
A: In this area you have five rings going around the circumference of the barrel. Since the this only needs to be smooth in one direction you could cut the number of rings down to one, this would reduce a lot of polys length wise.
B: At the end of tubes like this you can merge a lot of vertices together to cut out faces that the player (or networked players viewing you) will not notice.
C: The handle bar tube does not need faces on the end that is completely encompassed by other geometry.
D: Perhaps you intended for this to be a bullet that would be animated, if not, be careful of left over geometry that you no longer need.
