The advantage of the spool fed material is it's cheaper and you can honeycomb pattern the interior of models to save on supplies. The other advantage is if you're using PLA it's made out of natural starches, so it's more environmentally and health friendly than the liquid resins used in stereo-lithography machines.
The 15 micron figure is 99% probably the accuracy of the motors, not the endresult. And the 50-350 micron layer will sacrifice X/Y accuracy even more since it needs to melt the resin more to make the layer thinner, but as a tradeoff this makes each 'drop' a larger surface area. So no I don't expect this to be more accurate…