A typical marijuana "sack", or eighth(as in, 1/8 of a complete ounce. 1oz=28.35g, usually 28g in the dealing community), is 3.5 grams. So, 10 grams, would be a whole quarter ounce, plus 3 excess...
The standard price is $10 a gram, so, it would be reasonable to expect that you will get 1.5 grams for $15. However, if it's very high-quality weed, it might be more expensive. $15 might get you only...