Typically the directions for those nutrients is by the TEASPOON, rather than the tablespoon. So yes, you have prob been giving them a bit more than required. I would do water only for a week, as it sounds like you're adding a slow release which has prob built up over time and needs to flush out before you do any more feeding.
A couple other things to consider...
If you have the spare cash to spend, I can lead you in the right direction of buying nutrients designed more for the use of growing cannabis. Even if you don't want to make the trip to a hydro shop or order on ebay, there's still some cheaper options that you can grab from your local wal-mart garden dept or home depot. Your 15-15-30 NPK ratio is not ideal by any means, neither for veg or flower. An example of cheap things I purchased back when I was learning: Miracle Grow Organic Blood Meal (12-0-0) for veg, and their Bone Meal for Flower (5-12-6 or so). And just toss some bone meal in during veg to give it a lil phosphorus & potassium, then during flowering switch to bone meal only. That way your plants mainly get nitrogen during veg, and phos during flower. If you give your plant too much of something that it does not require in high doses, you risk causing nutrient lock, preventing your plants from absorbing the nutrients available to them that they DO need. So now that we got that out of the way, you can also spend a little bit more money if you want to get more scientific and purchase the following: PPM/PH meter - Measures your nutrient solutions parts per million reading and water PH levels, allowing you to either add more nutes if it's weak, or dilute with water if it's too strong. As well as allows you to add PH up/down to ensure proper 5.3-5.5 for hydro and 7.0 for soil. Better to be precise and follow a schedule of slowly stepping up the ppm for your plants as they mature. Next I would say take a hard look at Advanced Nutrients, Botanicare, or Roots Organics just to name a few of my favs. These are def pricier, but you will see amazing results compared to what you're currently using (everything from yield to taste & potency). It all comes down to what level you want to take your hobby to.
If you want help building a proper feeding schedule for your plants, as well as learning more about NPK ratios, micro nutes, carbs, bacterias, ... let me know