USB cable length

[bsf]

Does it effect sound quality have a long USB RUN (PC to DAC) I'm looking at around 15'

 

[PENG]

Does it effect sound quality have a long USB RUN (PC to DAC) I'm looking at around 15'

For that length you should use a booster/repeater.

 

[BoredSysAdmin]

USB max length by spec is 16 feet 5 inches. As for quality - it's irrelevant. It will work or not.
If you intend to use it for usb 3.0 full speed - you might have issues with mediocre cables, but audio usage - bandwidth requirements are negligible. If you want to sleep better at night get active usb cable, but it may not be necessary.