There are many answers to this problem, depending on your taste. Here's my answer:
With Q2 and Q3 running at 2mA, it would be convenient to run Q1 also at 2mA (so that its Vbe is similar). Thus, at "quiescent" conditions (i.e., VL=0V), RBIAS will have (15V-Vbe) across it, or roughly 14.3V. RBIAS=(14.3V/2mA)=7.2kOhm.
To ensure the voltage across Q1's Vce is 2Vbe, R1 should roughly equal R2 (neglecting finite beta), and most of the 2mA should flow through Q1. Let 200uA flow through R1 and R2. R1=R2=(0.7V/200uA)=3.5kOhm.
Next, run a simulation to confirm the accuracy of your calculations. My simulator shows 3mA flowing through Q2 and Q3, and 1.8mA through Q1. Not bad. Adjustments can be made to R1, R2, and RBIAS if you want to fine-tune things, but this is probably good enough.