The new object type for point clouds from ReCap (RCP/RCS point cloud) which can be attached to your DWG projects with functions of the plain AutoCAD cannot be yet used for terrain modelling in Civil 3D 2015.
Instead of this, load (attach) the point cloud using the standard Civil function, i.e. from the Prospector tree (as in version 2014). This function works with the original formats of indexed point clouds and it is possible to generate a terrain model surface and isolines (DTM/DGM) from these points.
If you already have your point cloud processed in the Autodesk ReCap application, export it from ReCap to the PTS format which is the supported in the Civil point-cloud function.
Another option is to use the tool "Point Cloud Surface Extraction" from the subscription module Civil 3D 2015 Productivity Tools (Subscription Center) - this tool supports ReCap point clouds.