Object identification is very slow

I encountered the same problem. As a workaround I gave up using Name Mapping. I mapped only the root container identified by the webpage URL. 

Every subsequent objects are retrieved by xpath in my project. And some container objects are manually "mapped" with xpath.

I created a function called "getContainer" which initialize a map with "key", "xpath".
then this function return the corresponding object. ( return page.FindElement(map.get("key")) ).

My function basically does the same thing as NameMapping, but mine is instantaneous. Not NameMapping.

If you don't use xpath, I think you can achieved a similar function with properties.
The best thing to speed up the retrieval of objects in this case (using properties) is to limit the level of searching (like 10 levels) and use some "checkpoint". 

For example : if your object is at the level 25, don't search directly for it, but search for a container few level above, then do a second search for your object using the container as starting point.