Corridor U follows US 15 from Williamsport to near the state line, but then turns abruptly east on PA 328 to end at Corridor T (I-86) near Elmira.
http://www.arc.gov/images/programs/transp/adhs_status_report_2010/ADHS2010StatusReportPennsylvania.pdf
http://www.arc.gov/images/programs/transp/adhs_status_report_2010/ADHS2010StatusReportNewYork.pdf
From the map and mileage (13.7 mi in New York) it appears to follow NY 14 all the way to I-86. The New York document shows that 2.7 miles were built with ADHS funds. Which part is this? The Clemens Center Parkway?
Looks like it.
In my opinion, US 15 should have taken a northeasterly turn after Mansfield, PA following PA/NY14 to I-86 at Elmira (basically along parts of U1). The entire route runs SW to NE, except the last section. It would make it more viable in my opinion.
^^^
However, US 15 used to go Rochester and detouring to Elmira along the way would add significant mileage to the route.
I can see what your saying that with it ending in southern NY, Elmira does look better than Corning.
Don't worry though, once I-99 is finished, US 15 may be truncated to Williamsport.