But that would give me less filtration at turning over my water 5 times per hour. Not 6.5
5 or 6.5 it doesn't really matter. There isn't really 65 gallons of water in your tank either. If you want to bump up the flow on the 2215s you can swap out the impellers for 2217 impellers. Also, don't run filter floss or foam in your eheims, it just clogs up super fast and slows them down. I just run coarse media in mine, you can let them run for a very long time this way.