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?
You are navigating away from the AIS Discovery experience