Not sure about the 15w vs 25w. I don't think this would really translate to LED bulbs. However, the only thing I can fathom is that the 15W bulbs have a more delicate filament, and your machine vibrates it to death. I *think* that lower wattage bulbs have longer filaments (= more resistance = lower wattage), so they probably have a longer length of filament between each support, so more there to bounce around when vibrated. It's just a hypothesis, though, and it probably depends on the engineering of that particular bulb.
That being said, however, if bulbs have been vibrated to death, LED bulbs may suffer a similar fate. Depends on the particular engineering, of course. Then again, that might've been the bad bearing, right? Maybe it's not even a concern now.