The application is on an usb thumb drive. therefore i dont expect an ultra fast browsing experience. it would be sufficient if it would run as smooth as within private windows.
Try removing everything from the drive and then putting everything back. When everything's off the drive, you can reformat it as NTFS (to rule out file system corruption or to convert it to NTFS if it was FAT32). I do that some times with thumb drives and it helps for a while.
I'm guessing that private mode is only faster because it's not using the disk as much.