I created a new class library (package) project (prior to VS 2015 RC used the even worse name of asp.net class library to represent the data layer. Just to be clear this is
Why does package manager think Enable-Migrations is invalid even though EF6 has been referenced?
Because I assume and am quite sure that ASP.NET 5 projects don't invoke install and uninstall PowerShell scripts inside the packages which EF 6 package has to add the migration commands to package manager console. Your best luck is to try to integrate the command line tool (I believe it is called migrate.exe, not sure) inside the EF6 NuGet package.