cut you model in half

There are programs that can reduce the polygon-count,

but better is to manually merge polys to reduce the polycount.
But that is work then of course.

Another way is to use the high-poly model as base,
and Model-around a new polygonmesh, using the
polys effectively to have a good shape with low polycounts.

In then end, a good texture is what counts, as a texture
can take up a lot of details that dont need to be modeled
then.