Help to calculate the collector current
When Q3 is activated you can assume that the base emitter voltage is 0.6 volts. This directly means there is 0.6 volts across R3 and this means the current through R3 is 0.6 mA.

For R2, the voltage across it is 15V - (0.6V + Vsat_of_Q2). I estimate that to be about 14.3 volts hence, the current into R2 is 14.3/3300 = 4.33 mA of which R3 supplies 0.6mA.