What if I water fasted for 13 days then took a 15 gram edible?
i wouldnt. you should avoid the muchies after that length of fast. its not a good idea to potentially overeat, as you risk refeed syndrome and you also risk constipation via overeating, as your gut motility will be too slow to handle solid food.
Shouldn’t be a problem by itself but you run the risk of eating a massive meal and trigger refeeding syndrome. If you’ve just taken the edible and aren’t sure how it will pan out I suggest breaking the fast with a small meal of steamed veggies now and prepare a healthy, balanced meal for later so that you have it ready when you’re high in a couple of hours.
I haven’t been in that situation, but I just want to add that apparently edibles work best when there’s a lipid element in your digestive tract to bind to, which won’t be present if you’ve spent the last two weeks fasting. So, possibly, you won’t feel it as strongly as you normally would, but I would still consider the concerns brought up by previous comments.