15PPM TDS is not safe for drinking. Because it will be lacking all essential natural minerals which are important for our health. Water contains some natural minerals in it which is essential for our body. Some of the most important minerals in water is: Calcium; Sodium; Potassium; Magnesium and more. read more
Yes it is completely safe but a TDS in the range of 35 ppm to 75 ppm is much better. RO water is normally in the above range. 15 ppm is getting close to distilled and you miss out on the much needed salts and minerals. Hope this helps. read more