I mainly do trans-pacific flights. In such long (>12h) flights I can't use wifi even if its on offer, as it chews through precious battery time too fast. I would kill for plane seats with power plugs, or even just USB power.
I once did London -> Chicago -> Seattle and still had about an hour of battery life for the bus from seatac. That wasn't continuous use, but as much use as I needed.
Not clear which exact model you have. Some have a discrete AMD GPU which would take more power.
Also it's not clear what format your videos were in. If it's something like DVD rips, then it could have been MPEG-2. I don't think Intel GPUs have any hardware support for playing that back. Also VLC probably doesn't take advantage of any CPU support for playing back video.
You should do a little more research. Your reported performance seems disappointing. You should be able to do much better. For example the current model 13" claims:
Up to 12 hours iTunes movie playback
Notice they don't mention VLC there. :) So you might have to transcode your video into a format that iTunes supports.