I can only speak to the northern third and the southern third. Rt. 15 north from Williamsport to the NY line is in excellent condition. From the junction with Rt. 581 in Harrisburg south to the Mason-Dixon Line is also good. There are a few portions just above Gettysburg that may have some "cratering" in the concrete slabs but nothing you can't avoid.
The last time I drove Rt. 15 from Williamsport south to I-80 was in March of 2012. It's a nice drive but you have a number of intersections and traffic lights in S. Williamsport and again around the Allenwood area.
Enjoy & safe travels.