R = \frac{U^{2}}{N}; R_{1} = \frac{12^{2} V^{2}}{15 W} = 9, 6 Ω R_{2} = \frac{220^{2} V^{2}}{15 W} = 3227 Ω

${R = \frac{U^2}{N}; R_1=\frac{12^2V^2}{15\,\mathrm{W}} = 9,6\,\mathrm{\Omega} R_2 = \frac{220^2 V^2}{15\,\mathrm{W}} = 3227\,\mathrm{\Omega}}$