I've installed the latest ArchiCAD IFC Revit Addin and it now takes 71/2 minutes for Revit to start (I timed it - 4 times). Normally it takes 18 seconds (I also timed that).
Latest open source IFC Export/Import Revit Addin is also installed (15.3.0.1)
Revit build: 20150511_0715(x64).
The addin works once Revit has opened, but we really can't use it in its current state.