Looking for a machine that can detect the underground 15 meters hollow

[Sunwei]

Good friends, please help me recommend a machine can detect holes, need a depth of 15 meters, can adapt to any terrain, including mountains, the site to see a treasure of Bulgaria's GPR do not know how the effect, please give me the most authentic opinion

[WM6]

Sorry, I have only machine for 57m depth. 15m is to shallow for my apparatus.