The question is a bit unclear, but I think you're asking: "Which travels faster: sound at 15°C or sound at 30°C?"

The answer is: Sound travels faster at 30°C.

Here's why:

* Sound travels through a medium (like air) by vibrations. The molecules in the medium bump into each other, transferring energy.

* Higher temperature means faster molecule movement. At 30°C, the air molecules are moving faster than at 15°C.

* Faster molecules transmit sound waves faster. Since the molecules are bumping into each other more frequently at higher temperatures, the sound wave travels through the medium more quickly.

Important Note: The speed of sound is also affected by the type of medium it travels through. Sound travels faster in solids than liquids, and faster in liquids than gases.