I’m not clear why you believe that intersecting polygons equates more polygons.
Additionally, this shape doesn’t need the polygons to go all the way through as it does. If this is a shelf of some kind, the shelves that are horizontal, could stop at the inner wall, the vertices should be flush to the surface. This isn’t about cutting down on polygons but rather eliminating artifacts in game.
When you are modeling, don’t count the polygons by eyeballing them. A polygon doesn’t get subdivided because it intersects another shape, unless you do something to it, which usually involves other steps to your modeling like creating boolean shapes.
Look at the polygon/triangles reported for your object in your modeling system. In Maya it is reported in the upper left of your screen when turned on.
Display -> Heads Up Display -> PolyCount
When you import your fbx into UE4, the triangles will match. You model in polygons, but game engines want to break that into triangles. So the reported triangles in the HUD of Maya, will match exactly the triangle you see on your model when it is imported to UE4. You can see that number when it is importing, and when you edit that model in UE4, in the upper right corner of the Details panel associated with that model.
If you are getting 254 polygons for an object like this, there is something oddly wrong in your technique, or possibly your software that you are using that it would do this. Is this possibly Sketchup?
(in other words you should be able to make that shape you have in 48 polygons, 96 triangles).