Logic-level switching 12v
A BJT transistor's pass-thru voltage will never rise above base voltage; thus the 4.34V &amp; also why you place it between a resistor and GND, rather than drive 1 transistor directly through the other.
The resistor allows you to 'invert' and amplify the voltage change of the incoming signal. When Q14 is 'open,' R15 allows the base of Q15 to reach near the 12V source voltage.
When Q14 'closes,' it 'shorts' the charge between R14 &amp; itself to GND, so the base of Q15 'sees' a minimal voltage. If R15 were absent, then Q14 would have little/no effect on Q15's output, but in this way, turning 'on' NPN Q14 lowers base voltage to PNP Q15, enabling it to pass power through to your load.


Alternately, you could accomplish the same/similar end result with a single N-MOSFET this way:

(sorry, my schematic app cut the 'd' off of "Load")