Some people do like silica gel, but for larger time capsules, we prefer to use desiccant. You will need more silica gel than the desiccant. I can tell you that we provide 10 units of desiccant for our 16x16x20" time capsule. However, that is a different unit of measure than the grams of silica gel. If you use silica gel, in general you would cover the bottom of your container, in the instance of a 15 inch high one, about 3". And this would be in bulk. I'm sorry I cannot make a better estimate at this time. Best of luck to you!