I just did a spot check on our low-sugar smoothie recipes and did not find anything that would be greater than 20g of sugars.
Go to: https://www.nutriliving.com/recipes/
Check the box, "low-sugar" and all recipes should be 20g of sugars are less.
15g of sugars equates to 1 Carbs which is not a lot of sugars in comparison to other to other food products. If you are concerned about 15g of sugars, we would recommend using more vegetables and fruits like berries that are higher in fiber. Other things to add to your smoothies that would slow the sugars from entering your blood stream are healthy fats and plant-proteins like nuts, seeds, and avocados.