I absolutely would not even come close to considering such, just sounds like an accident waiting to happen. Plus the fact it would have to be a stainless steel pressure cooker, and I just cannot see any point to cooking soap under pressure. Do remember the escaping steam is going to contain lye. I would not even consider it in my large canner that has very heavy duty lockdowns for the lid. The average pressure cooker is just not completely reliable either. Not sure why it takes you so long and I do not do a lot of hp, not my favorite type of soap, but it only takes me about 20 min max