Honestly if you say the DVD-R failed to load, but yet the game works on USB with slow loading times, I guess you'd have to bear with it
I'm not sure if a internal HDD may be faster though, but that's only for FAT PS2
ps2 is only usb 1.1 thats why it's so damn slow on loading times. if you have a fat ps2 you can get a hdd adapter and put ide (or with special adapter, sata) HDD inside and load from that, it's much faster.
You could even go Sata2SD and use a big SD card, less power consumption and no HDD noise