2009 8 Core RAM Upgrade Question

I have an 8-core 2009 Mac Pro with 6 1GB sticks of RAM. I just ordered (3)x4GB of RAM from OWC. My thought was to do the 3X4GB and 3X1GB for a total of 15GB of RAM.

Does this make sense? Is this best use of my existing RAM? Will I take any performance hit?

Any advice is welcome.

 

Thanks. Appreciate the response and your other posts. You've been helpful a number of times outside of this thread.