It's not possible to install using \gs\gs9.15\lib\ghostpdf.inf Apparently the issue occurs as the printer driver is not signed... Is it possible to acquire a signed printer driver for GhostScript? Or is there a work around to install the driver?
ghostpdf.inf is not strictly part of Ghostscript and is provided as a convenience. You will need to update to the forthcoming 9.18 release, due in a few weeks. See commit be72694a3cac0aa72c0843334e7f1afdabbddc7a This is hardly a major problem.