It felt smoother with the 12 balls. With the 15 balls, it was strangely gritty, like it was just running on the 3 balls and the other 12 were disengaged. It was just an experiment for me as I only had 24 balls (so I borrowed 3 from the other diff while I messed around building the first one). These were ceramic balls from JAAD.
The problem was very likely just the plates. I don't remember if I ran new ones or flipped them around or just chucked the new balls into the old grooves. I think they would work after breaking in, but with the 37 tooth pulley, I figured the extra 3 balls so near the centre wouldn't have made a huge difference so I didn't bother ordering more balls.
Some of my friends who run the TRF415 swear by the extra balls though. I think they go from 8 balls to 16 though (TA-05 original pulley, 501X ring), so that's a huge jump in ball count (that's an official term)
