I agree that this is wrong. I use the same paper and I think I have 150w bulb. I usually get around 15s at f5.6 or f8 (I could check my notes, but one of the two) for 10 x 8"-ish enlargements.
Have you got one of those (e.g. Schneider Componon S) lenses with a lever that overrides (opens up) the aperture setting whilst focusing? i.e. Could you be printing at f2.8 or 4 without knowing it? As mentioned the bulb wattage if the other thing to check.
You shouldn't need to shut down to f11 or beyond so something needs fixing. Of course, ND filters would work but I kind of feel that that would be a bodge instead of understanding the cause.