With v2.18.2:
Starting lilypond-windows.exe 2.18.2 [marcMultiRestStencil.ly]...
Processing `C:/Users/Pierre/Documents/LilyPond/0 help/marcMultiRestStencil.ly'
Parsing...
Interpreting music...
Preprocessing graphical objects...
Interpreting music...
Preprocessing graphical objects...
Finding the ideal number of pages...
Fitting music on 1 page...
Drawing systems...
Layout output to `marcMultiRestStencil.ps'...
Converting to `./marcMultiRestStencil.pdf'...
Success: compilation successfully completed
Completed successfully in 1.1".
With v2.19.47:
Starting lilypond-windows.exe 2.19.47 [marcMultiRestStencil.ly]...
Processing `C:/Users/Pierre/Documents/LilyPond/0 help/marcMultiRestStencil.ly'
Parsing...
Interpreting music...
Preprocessing graphical objects...
Interpreting music...
Preprocessing graphical objects...
Finding the ideal number of pages...
Fitting music on 1 page...
Drawing systems...
Layout output to `./tmp-lilypond-gB6KlR'...
Converting to `marcMultiRestStencil.pdf'...
Deleting `./tmp-lilypond-gB6KlR'...
Success: compilation successfully completed
Completed successfully in 20.6".
so roughly 20 times longer...