Actually, I have some good news.. I hope this helps you
Many cases of bacterial kidney diseases can be successfully treated. Leptospira is one bacterium that can cause acute renal failure. Other bacteria can also cause kidney infections, invading the urinary tract, the bladder or prostate for example, and ascending up to the kidneys. With proper diagnosis and treatment these infections can be treated effectively with antibiotics and, in most cases, result in complete recovery.
Ingesting as little as a teaspoon of ethyleneglycol-based antifreeze, which forms crystals inside the dog's nephrons and shuts down kidney function is usually fatal. Unfortunately, this product has a sweet taste which attracts pets to drink it. (Propylene-glycol-based antifreeze is a safer way to protect your car and your dog.) Another potentially lethal substance is rat poison. If a dog eats rat poison containing calciferol (a form of vitamin D) the calciferol pushes up the dog's calcium level, causing mineral deposits, inflammation, and other damage within the kidneys.
Ironically, treatments for some nonkidney diseases can jeopardize the kidneys. Although most antibiotics cause no harm to the kidneys, practitioners should closely monitor patients on certain antibiotics - gentamicin, for example - because of potential damage to nephrons. Cisplatin (an anticancer drug) and amphotericin B (a drug for serious fungal infections) can also cause acute kidney damage. In general, before you decide on a course of treatment for any condition, ask your veterinarian about the benefits and risks of all available options.
Unfortunatley, since your dog is 15 there will most likely be more illnesses to come. Please don't commit suicide over this, that is not what your dog would want for you. I really do hope he get's better, and Good Luck. Don't feed him any foods that are bad for him to begin with. Please write us back and let us know how he's doing. Good Luck :)