A store carries a popular food item. The average demand for this product is $15$ units per day, with a standard deviation of $3\mathrm{.}5$ units. The stock is checked weekly. Suppose that at one particular occasion when the stock is being checked, there are $5$ units in stock. The lead time to receive an order is $3$ days. If the store wants to maintain a $95\%$ service level, then the order size for this period is $\_\_\_\_\_\_\_\_\_\_.$

Group of answer choices

$163$

$164$

$166$

$167$