I didn't notice any slowdowns when creating 15 clips. But my system has 32 GB of RAM.
A while back, I noticed improvements in CinGG's responsiveness by setting:

1- Settings --> preferences --> performance --> Cache size (MB): 4096
2- Settings --> preferences --> performance --> Seconds to preroll renders: 1.0000

This probably isn't related to your problem, but it might help to set these parameters optimally for your “Charlie.”