How to make my objects see through (SOLVED)

That would work, too @augold45 . But sometimes decimate acts in weird ways and can cause tears in the mesh. If you start as low poly as you can while still maintaining something that looks decent in game, you won't run into that tearing issue.

I haven't found that removing doubles typically reduces polys (tris) by very much. It often reduces the number of vertices, but not necessarily polys.