LC filter for Vref and Vadc
The rolloff frequency of a LC filter is \$ f = \dfrac{1}{2 \pi \sqrt{LC}}\$.

When L is in Henries, C in Farads, then f is in Hz.  This comes out to 15.9 kHz for 10 &micro;H and 10 &micro;F, so your simulation is apparently correct.

Just like RC filters, LC filters can be arranged for frequencies over a wide range since inductors and capacitors come in a wide range of values.  They are not inherently "high" or "low".

Often the DC level of a power supply is pretty good but has high frequency noise on it, like from a switching power supply and high frequency components of switching transients.  Sometimes these are filtered with a small chip inductor in series followed by a ceramic cap to ground.  The rolloff frequency may be a few 10s of kHz, but the noise is much higher than that.  Lots of analog chips have pretty good power supply rejection capability, but since this is done with active electronics it fails at high frequencies.  As long as the power supply filter removes the high frequencies the electronics can't handle, things will work well enough.