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Coupled walls are for when you have cells on both sides of a wall, ie it's part of a conformal mesh. Rather than use ancient documentation I strongly recommend using the Help system within the software. 

Without seeing any of the mesh & geometry I can't comment. Assuming you do have many cell zones and also added several local sizing commands and/or size functions Ansys Meshing has to evaluate all surfaces/settings to all other surface/settings prior to creating the mesh: that tends to slow things down. 

Re mesh independence, have you read up on mesh adaption (refinement) in Fluent? For mesh creation, will Fluent Meshing speed things up?