Final answer:
The expected gain in SPL at listener #1's position depends on the inverse square law of sound intensity, but a specific value cannot be calculated without the initial SPL.
Step-by-step explanation:
Understanding the expected gain in SPL (Sound Pressure Level) at different distances from the source requires knowledge of the inverse square law for sound intensity. SPL is a measure of sound pressure relative to a reference value and is measured in decibels (dB). The intensity of a sound wave decreases with the square of the distance from the source. Therefore, if listener #1 is 2 meters away from the presenter and listener #2 is 15 meters away, we calculate the gain in SPL, taking into account that it is inversely proportional to the square of the distance. The gain in sound intensity level is calculated by comparing the intensity levels at the two distances using the formula 20 * log10(distance2/distance1), but since the question does not provide information about the initial SPL, we can only describe the method but not provide a specific gain value.