I can't think of a situation where there is such a thing as too much sub. You can always drop the level of a beefier sub, but the opposite can't be said for a sub that is insufficient for the space. Without looking at the chart for the E15, what you'd gain with it would be nearly twice the power and likely a significant gain in output over the F12, so if this is for moderate volumes, the F12 is likely enough, especially if the office is a room that can be closed off and is not open to other areas. If money is not a big factor, I'd personally still opt for the E15 simply because it will likely handle a wide variety of rooms besides just the office.
I realize this is for music, but these are servo subs and as such, even the vented Rythmiks are still likely to do very well in that department; just not as well as the sealed ones.