I have 2 setups, both connected to an NFS mounted NAS via wired gigabit ethernet, one of which stutters. The one that stutters is a beaglebone black connected to an audioquest dragonfly, which accepts up to 96kHz sampling rates only. This produces stutter (both with Volumio 1.4 and 1.5) with any source material that exceeds 96kHz. I briefly had the beagle hooked up to a dac which only accepts 48kHz through its USB input, and that similarly suffered stutter with >96kHz music.
Because of this I guessed that Volumio’s downsampling was working properly, and it might be down to USB quirks, RAM and/or processor power. so I bought a Cubox i4pro, which had 4x the RAM, way faster processor and the ability to connect up via toslink. It’s connected to a Cyrus DAC via toslink so I can take advantage of full sampling rates up to 192kHz. This has so far behaved perfectly. I haven’t had a chance to investigate whether it’s a USB thing yet by connecting the dragonfly to the Cubox, but one of these days I will. In the mean time I would love to hear what others think.
Bottom line, though – wifi sucks, and there’s probably no substitute for RAM and processor speed in the long run. Have you ruled out completely that it’s the fault of 1.5? Have you gone back to 1.4 to verify this?