Looking at the operating system support for Civil 3D 2015, it seems that Autodesk have completely dropped 32bit support for Civil 3D 2015 – check out this link
Copyright 2014 (c) Longbow Software
Longbow Software Blog
by Simon Booth
Looking at the operating system support for Civil 3D 2015, it seems that Autodesk have completely dropped 32bit support for Civil 3D 2015 – check out this link