Having built and flown countless .19 powered planes, I'd definitely use .012's. Way less draggy on the smaller models and will allow a bit more line length than .015's.
For line length, I'd probably start at around 56'-58'. You can always shorten lines if you need to, but that's going to be pretty darned close.
But just for fun, I'd like to see you try to fly it on set of .015x15' lines, as per your OP question.
....and if you do it, please get it on video.
