What was the longest echo and how long did it last?

It is constructed of marble and sandstone and is surmounted by a dome 36m in height, with two main spaces, a crypt in the lower section, and a chapel that was supposed to be used for worship. However the construction materials, size, shape and dimensions of the latter result in a complex, dense and very long reverberation, and hence render it almost useless for speech presentation. In fact the Guinness Book of World Records claims that the Hamilton Mausoleum has the longest “echo” of any building, recorded on 27 May 1994 as taking 15s for the sound of the reverberation caused by slamming one of the main doors to die away to nothing.