Visual Studio "15" = Visual Studio 2017 = VC 15.0 Crystal clear. Why didn't Microsoft bump up VC version to 17 to sort of make VC version follow VS version. Would clear out some confusion going forward.
Many software packages have poor or confusing version numbering. Java, IIRC, jumped from Java 1.2 to 2 or 1.4 to 4 or something like that. Windows 3.1 to 95 to 98 to Me to NT (stood for New Technology, ha ha [1]) to 2000 to XP to Vista to 7 to 8 to 10 ... (might have got some of the order wrong there). [1] New, as in the classic marketing/advertising phrase "new and improved", maybe ... :)
Also, NT came before 95. Specifically, as Windows NT 3.1.