Explanation: 15 kHz falls within the Very Low Frequency (VLF) band (3 kHz to 30 kHz). VLF radio waves are used today for specialized long-range communication, such as communicating with submerged submarines due to their ability to penetrate seawater, and for transmitting highly stable time signals (e.g., WWVB at 60 kHz). These are among the lowest carrier frequencies regularly employed for radio communication. Options A (SSB voice) and B (Double-sideband FM voice) describe types of modulation, not specific frequencies. While these are used in radio, their carrier frequencies are typically much higher (e.g., kilohertz to megahertz for SSB on HF, megahertz for FM on VHF/UHF). Option D (1 kHz to 5 kHz) is primarily within the audio frequency range. While these frequencies are components of speech, they are generally not used as carrier frequencies for radio transmission. Efficient electromagnetic radiation for communication over meaningful distances typically requires carrier frequencies of 9 kHz and above, which is where the internationally recognized radio spectrum begins.