SU 6175 appears to be a re-purposed ashlar block, likely spoliated from another, earlier, phase of room G-1. In its current position it seems to serve as part of the foundation for a pier (SU 6127), along with SU 6174 and SU 6176, and likely part of the same phase of construction.
Room G-1 center-west
SU 6162, SU 6174, SU 6175, SU 6176. Photo taken from the north.