1. Identify the principal amount: P = 6000.
2. Convert the annual nominal rate to a semiannual rate: r = 0.15/2 = 0.075.
3. Convert the time period from bi-monthly to half-years: n = 2/6 = \frac{1}{3}.
4. Apply the simple interest formula: I = P \times r \times n.
5. Calculate the interest: I = 6000 \times 0.075 \times \frac{1}{3} = 150.
The interest to be paid is 150.