C

Step 1: The photoelectric current is directly proportional to the intensity of light incident on the photoelectric cell. \
Step 2: The intensity \(I\) of light is related to the focal length of the lens. If the power \(P\) of a lens is given by \( P = \frac{1}{f} \), where \(f\) is the focal length, then for two lenses of different focal lengths, the intensities can be related.\
For the first lens, with focal length of 30 cm: \( P_1 = \frac{1}{30} \)\
For the second lens, with focal length of 15 cm: \( P_2 = \frac{1}{15} \)\
Step 3: The ratio of the intensities (and thus the currents) can be expressed as \( \frac{I_2}{I_1} = \frac{P_2}{P_1} = \frac{\frac{1}{15}}{\frac{1}{30}} = 2 \)\
Therefore, if the current produced by the first lens is \(I\), the current produced by the second lens will be \(I_2 = 2I\), thus matching Option C: \(2I\).
Therefore, C.