wow, now that is some flow. so in other words 15X is inadequate.
Based on your signature.... for the contents of your tank 15X is fine if you are not noticing any crap collecting... try to remember to clean your rockwork every once-and-a-while with a turkey baster and you'll be fine.
If you are looking for more nutrient poor systems then it is beneficial to have lots of flow... I plan at least 50X turnover for my BB 120