Real-time network simulation enables simulation to operate in real time, and in doing so allows experiments with simulated, emulated, and real network components acting in concert to test novel network applications or protocols. Real-time simulation can also run in parallel for large-scale network scenarios, in which case network traffic is represented as simulation events passed as messages to remote simulation instances running on different machines. We note that substantial overhead exists in parallel real-time simulation to support synchronization and communication among distributed instances, which can significantly limit the performance and scalability of the hybrid approach. To overcome these challenges, we propose several techniques for improving the performance of parallel real-time simulation, by eliminating parallel synchronization and reducing communication overhead. Our experiments show that the proposed techniques can indeed improve the overall performance. In a use case, we demonstrate that our hybrid technique can be readily integrated for studies of software-defined networks.