Lowpass Filter and Attenuator
Trying to answer my own questions:


I haven't found out if this is necessary at all yet.
Apparently I was not going about it the right way. The filter I designed attenuates the 15kHz portion of the voltage by 10 dB, but it does not attenuate the DC component and so the voltage at the ADC input is much larger than is permitted. As far as the DC component is concerned, this is only an averager, not a divider.
See 2.
The advantage to the circuit posted in the question I linked is: it actually does what I want it to.