PyInstaller creates slow executable

Question

I'm using PyInstaller to create a single executable of a python program using PyQt. It creates the .exe and runs fine, but takes between 15 to 20 seconds to start. I thought I could get by with creating a splash screen so the user would at least know something was happening, unfortunately, the splash screen doesn't show up any quicker than the program window itself. I also created the same program as -onedir, the program does start quicker, but this isn't really an option for distribution. If anyone has any ideas on what is slowing down the execution and ways to speed things up I would certainly appreciate it. Thanks.