If mesh is made out of quads in edit mode, select the mesh, then ctrl+e and choose Un-Subdivide
Delete Edge Loops
Quite common tactic to reduce poly count in oval shapes objects.
In edit mode select edge loop by pressing alt+right click, then space and type Delete Edge Loop
One of my favorite and quickest techniques. Quickly remove unnecessary vertices without breaking the mesh structure. Still might require some manual adjustment but dramatically reduce poly counts.
We reduced poly count from 49,216 to 436. You can also play with max angle value under limited dissolve menu. It works well on square objects with lots of edge loops.
Select object and add Decimate modifier
9750 polygons on the the top photo vs 436 after using decimate modifier.