Hey, heyyydeelee!
It could be many things causing the low FPS. Without any information about your system, it is hard to say. I would first recommend deleting the Documents/Overwatch/Settings folder to see if it helps at all. Make sure to default your graphics driver settings in your Nvidia settings also.
If this does not help, please make your own thread with your DXDIAG and we can take a look. Use the Preformatted Text button in the posting options.
I will be locking this thread to avoid confusion as it is older.