LAYMRG is an Express Tool that I use to fix drawing that have way too many layers.
It moves all objects on the first layer selected onto the second layer selected. The first layer will be deleted and purged from the drawing.
Issue the command and select an object or objects that are on the layer(s) that you want to move (merge) to another layer.
All of the objects on the selected layers will be moved to the new layer. The layer names that were used will be gone from the layer dialog box.
It works quite well.