Hello, Frank.
For "automatic" interpolation I use same name function:
Func = Interpolation[DataTable, InterpolationOrder -> 1];
I also tryed to write manual procedure using:
Needs["TetGenLink`"]
TetGenDelaunay[MeshNodes]
RegionMemberFunction
NearestFunction
Due to Delaunay mesh size (~1.3m tetrahedrons) this option may take more time.