Single transistor buffer and low pass filter
You are over-thinking this.  Here is all you need:



This satisfies all your specs:

have high input / low output impedance.

The input impedance is 2.2 k&Omega; and the output impedance 550 &Omega;.

divide the signal by 2.

It does that, since it is basically a resistor divider with two equal resistors.

low pass filter the signal (cut freq. = 15KHz).

Assuming you really mean kilo-Hz, not Kelvin-Hz as you wrote it, this is accomplished by C1 working against R2.  The rolloff frequency is

&nbsp;&nbsp;1 / (2 &Pi; R C) = 14.5 kHz

which is within 4% of the target, and considerably less than the tolerance of ordinary parts.

This circuit has additional advantages over something like what you show:

The gain is more accurate since there is no additional attenuation thru a emitter follower.

It doesn't require power.

It is more linear.  The B-E voltage of your circuit isn't completely fixed or a linear function of the output voltage.  As a result, the emitter follower is slightly non-linear.