7.5 is functionally a voltage limit but phrased by cell count. If you are using 2 batteries you wouldn't be wiring them in series, they would be separate circuits (With a max of 12 cells in series so fine).

Basically as long as you aren't arranging your battery packs in any way that puts more than 12S in series you're fine. You could have 6 12S packs and as long as they are all in parallel it's fine.