I doubt the issue is with low yields of those 15 core tiles, if it is and they cant consistently produce more than 4-6 functional cores per tile (despite producing 18 core chips or more since like 2014), then they are doing it wrong. I think the issues are more likely with the stacking part of the chip.As for SPR, IIRC Intel last said the launch would be in 1H. Which of course ends in 9 days. They could still do it but if they aren't even going to ramp for another 6+ months... that feels wrong. I suspect they will make a delay announcement this week but they will just have to pick the right day.
If they are only mostly getting 4-6 cores per tile I'd be tempted to go ahead with the W launch anyway given that the volume is low and Icelake-W never got any traction with the big OEMs.
If they have already named SKUs of those chips, like that 16 core part leaked yesterday on wccftech, perhaps they are going ahead with that W launch.