For the record, that i5 NUC might benefit from the PPA here: https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers
I track it and my (purely seat of the pants) performance seems to be slightly better in games. That PPA provides an continuously updated graphics stack (mesa and all-vendor drivers) and since the HD 6000 graphics on the i5 Broadwell is fairly new, my thinking is that they are still doing optimizations for it.
That said, stability and performance were absolutely fine with the default 15.04 setup. Also, the i3 version’s graphics solution has been around a while, so I’m not sure the PPA would do it any good.