I have a 1M SPDIF, and it works just fine, I haven't heard of the 1.5M being the ideal length. But YMMV.
Length of SPDIF cable
I've just ordered a Xangsane pure silver SPDIF coax cable and it's already on the way. I've ordered a 1m cable because I've read that "you should not have a too short SPDIf cable". My previous ones were all 0,5m.
But now I read that the ideal length would be 1,5m which kinda makes me wonder if 1m is not just the "wrong" length.
Well I will listen to it, I suppose if it sounds good it's good, but still, why don't they only make 1,5m coax cables if that is the recommended length?!?