id say if you take 15 grams thers a high risk of dieing.
Based on what do you think 15g is a lethal dose?!
Sure, you'd trip your pants off, possibly pass out, maybe throw up, but personally I really don't think you'd die.
If anyone knows of a case where the cause of death has been isolated to proper magic mushrooms, please post!
But anyway, you're right: the most likely way to die is if you eat the wrong kind of shrooms. "Know your source."
In fact, here is an extract from the very anti-drug site http://www.recovery.org.uk. These guys really try hard to make all drugs sounds bad, and this is what they cam up with for psilocybe shrooms.
"
Psilocybe mushrooms are not poisonous in the sense that no lethal dose is known. However, some people react to them with vomiting, nausea and stomach pains. No serious long-term physical damage to health has been reported although it must be noted that no research has been carried out to assess the effects of frequent use.
The main risk to health from eating philocybe mushrooms comes from mistaken identity - collecting and eating poisonous varieties of mushrooms instead of the ones possessing the desired hallucinogenic properites. Some of these other fungi can cause death or permanent liver damage within hours of ingestion."
Note that non-psilocybe magic mushrooms can contain quite destructive poisons along with the psychoactive components, so they have 'easily achievable' lethal doses.
Also check this page for information on the toxicity of magic mushrooms: http://www.shroomery.org/index/par/12208