Calculate(i)the rate of energy consumption (ii)the total heat energy developed in 15mins in the circuit above

The formula for two resistors in parallel is $R_p = \frac{R_1 \times R_2}{R_1 + R_2}$.

$$R_{parallel} = \frac{4 \, \Omega \times 4 \, \Omega}{4 \, \Omega + 4 \, \Omega} = \frac{16 \, \Omega^2}{8 \, \Omega} = 2 \, \Omega$$

The total current flowing into the parallel combination is $I = 2.5 \, \text{A}$. The formula for power is $P = I^2 R_{parallel}$.

$$P = (2.5 \, \text{A})^2 \times 2 \, \Omega = 6.25 \, \text{A}^2 \times 2 \, \Omega = 12.5 \, \text{W}$$

The rate of energy consumption is $\boxed{\text{12.5 W}}$.

The formula for heat energy is $Q = P \times t$, where $P$ is the power calculated in part (i).

$$Q = 12.5 \, \text{W} \times 900 \, \text{s} = 11250 \, \text{J}$$

The total heat energy developed is $\boxed{\text{11250 J}}$.