The simulation seems to run much slower in 2D mode than before. What could be the reason?

The 2D visualization during a simulation run can be slow on Windows 7® if a desktop theme with Aero (translucent glass design) is selected. If a basic theme without Aero is selected (in Control Panel - Appearance and Personalization - Personalization - Theme), the 2D visualization can be up to 9 times faster.