It's about one-and-two-fifths times as deep as The Challenger Deep (Marianas Trench)
In other words, 15 kilometers is 1.3759 times the depth of The Challenger Deep (Marianas Trench), and the depth of The Challenger Deep (Marianas Trench) is 0.7268 times that amount.(near Marianas Islands, a.k.a. Ladrones Islands, northwestern Pacific Ocean) (depth below sea level)
The Challenger Deep, at the southern end of the Marianas Trench, reaches a depth of 10.902 km below sea level. The first manned expedition to the bottom of Challenger Deep took 4 hours and 48 minutes in 1960. This was the only manned descent to the floor of the Trench until 2012, when director James Cameron made the trip; several other descents have been made since then.
It's about one-and-two-fifths times as tall as Maxwell Montes
In other words, 15 kilometers is 1.4 times the height of Maxwell Montes, and the height of Maxwell Montes is 0.71 times that amount.(Ishtar Terra, Venus)
Maxwell Montes rises to a total height of 11 km. Since Venus does not seem to have the kind of tectonic activity which gives rise to mountains on Earth, the origin of the Venusian mountain remains the subject of some dispute.
It's about one-and-two-thirds times as tall as a Mauna Loa
In other words, 15 kilometers is 1.636 times the height of a Mauna Loa, and the height of a Mauna Loa is 0.6112 times that amount.(Hawaii) (Hawaiian island volcano) (total height from seafloor)
Mauna Loa, one of the five volcanoes which forms the island of Hawaii and the tallest mountain in total height in the world, rises to 9.20 kilometers above the seafloor. The peak of Loa is home to the approximately 6,000 sq. m (0.6 ha) Lake Waiau, one of the highest altitude lakes in the United States outside of Colorado.
It's about one-and-seven-tenths times as tall as Mount Everest
In other words, 15 kilometers is 1.69513 times the height of Mount Everest, and the height of Mount Everest is 0.589925 times that amount.(a.k.a. Mount Chomolungma, a.k.a. Sagarmatha, a.k.a. Mount Qomolangma, a.k.a. सगरमाथा, a.k.a. Chajamlungma, a.k.a. ཇོ་མོ་གླང་མ, a.k.a. 珠穆朗玛峰, a.k.a. Zhūmùlǎngmǎ Fēng) (Sagarmatha Zone, Nepal and Tibet, China) (to summit, excluding snow depth)
Mount Everest rises 8.848860 kilometers above sea level at its summit. The plate tectonics of the Indian subcontinent continuously alter the mountain's peak â€” raising it by 0.00000400 kilometers and shifting it to the northeast by 0.00000450 kilometers each year.
It's about three-fifths as tall as Olympus Mons
In other words, 15 kilometers is 0.56 times the height of Olympus Mons, and the height of Olympus Mons is 1.8 times that amount.(a.k.a. Mount Olympus) (Mars)
The tallest mountain in the solar system, Olympus Mons rises to approximately 27 km. The mountain has been known to astronomers since the nineteenth century because it is tall enough to rise above Mars' frequent dust storms.
It's about two times as long as Calangute Beach
In other words, 15 kilometers is 2 times the length of Calangute Beach, and the length of Calangute Beach is 0.5 times that amount.(Goa, India) (approximate)
One of the most popular tourist destinations in Goa, Calangute Beach, the "Queen of Beaches," stretches about 7 km in length.
It's about two times as tall as Aconcagua
In other words, 15 kilometers is 2.1546 times the height of Aconcagua, and the height of Aconcagua is 0.46412 times that amount.(a.k.a. Cerro Aconcagua) (Mendoza, Argentina)
Aconcagua measures 6.96190 kilometers height at its peak. Although there is no definitive evidence that members of the indigenous Inca civilization ever reached the peak the mountain, numerous archeological sites have been found on the slopes of the mountain, including a naturally-embalmed Incan mummy was discovered on a 5.20 kilometers high ridge.