Truffles are less potent than mushrooms, so you need to more or less double the dosage. I would think that the 15 grams of truffles then would be equivalent to about 7-8 grams of dried mushrooms. Since it was ingested throughout the day, I would assume that's dosages equivalent to 1-3 grams spread out through the day.
> I would think that the 15 grams of truffles then would be equivalent to about 7-8 grams of dried mushrooms
Spread throughout the day that would be reasonable for a facilitated retreat, yes. Also depends on the variety, some strains can be extremely powerful, to the point that 3.5 grams is more than enough.