The installation of MySql on Windows may lead to invalid PATH environment variable. The installation also installs some tools in a sub directory „MySQL Fabric 1.5 & MySQL Utilities 1.5“. This path is also added to the PATH environment variable which leads to something like

PATH=C:\Python27\;C:\Python27\Scripts;C:\Program Files\nodejs\;C:\Program Files (x86)\MySQL Fabric 1.5 & MySQL Utilities 1.5\;C:\Program Files (x86)\MySQL\MySQL Fabric 1.5 & MySQL Utilities 1.5\Doctrine extensions for PHP\;C:\Program Files\Microsoft\Web Platform Installer\;C:\Program Files\Git\cmd;

The ampersand characters in the path entries are not escaped and thus will be evaluated when the PATH variable will be used in shell commands, for instance when the PATH variable is extend like set PATH=%WindowsSdkDir%bin\x86;%PATH%. This is used in Visual Studio 2015 Developer Command line (VsDevCmd.bat) and this is the reason for errors when running the „Developer Command Prompt for VS2015“:

'MySQL' is not recognized as an internal or external command,
operable program or batch file.

The solution is modify the path in the system settings and use 8.3 paths for the problematic paths. To get the 8.3 path open a command shell, change to the containing directory „C:\Program Files (x86)\MySQL\“ and execute dir /x. In my case the short name for „C:\Program Files (x86)\MySQL Fabric 1.5 & MySQL Utilities 1.5\“ was „C:\Program Files (x86)\MySQLMYSQLF~1.5\“, on your system it is probably different.