Better in this case is very subjective. Only you can
decide which sounds better.
With that said, the Luxman R-115 is a wonderful stereo
receiver with a top notch tuner on board and plenty of
neutral/warmish and detailed ooomph to mate with many a
speaker.
If the question was the R-117 vs the 7175PE, the R-117
would most likely get the nod every time. As a matter of
fact, the
Luxman R-117 is often considered the finest stereo
receiver produced after the receiver wars of the 70's.
It has legendary status.
The R-115(70w/ch) is built to the same standards as the
R-117(160w/ch) but with less power. It also
"could" be considered the 2nd best receiver of
the 80's.
I have plenty of experience with NAD gear but the 7175PE
is one piece I have never heard.
Bill