If you have a 15''/17'' 2011 MacBook Pro with the dual GPU configuration (AMD Radeon HD 6490M/6750M/6770M) you may get better performance by forcing the discrete GPU with an app like gfxCardStatus or in System Preferences > Energy Saver.They are missing modern features and more/faster shader units which GLideN64 takes advantage of. Performance with GLideN64 may improve over time for old GPU's, but that is unlikely.Your issue isn't Mupen64Plus running slow, but the current iteration of GLideN64 used which your old/slow GPU (Intel HD Graphics 3000) has issue with.

Parallel N64 is a modified version of Mupen64Plus, featuring a Vulkan-optimized renderer which will provide no benefit on Mac, especially your 2011 MBP with an old/slow GPU (Intel HD Graphics 3000) that does not even support Metal or Vulkan. We only support stable release Mupen64Plus paired with the GLideN64 GPU plugin as our main N64 core plugin.