Don't be concerned. I had a similar situation occur... 15 apps, no acceptances and only 2 interview offers.
Of those schools, I reapplied to several again. I also applied to some additional schools, and dropped a few that I didn't have a real chance at the first time through but was reaching for the stars on (e.g. Yale.)
Year 1: Interviewed by Oklahoma State University and Michigan State University.
Year 2: Offered interviews at 14 schools, accepted 8 interviews, and was accepted at 3 schools that I really liked, one of which was my number 1 choice that year.
I was accepted at University of Maine, Texas A&M, and Uniformed Services University. It was crazy the difference a year made.
While I was not accepted at a few schools that I really liked (University of Alabama and University of Kansas) I was interviewed at both and was quite competitive. I was also invited a second time to MSU for an interview, which was great. I was also turned down by some lessor schools... how that happened, I dunno, but I really didn't care to be honest.
So keep your head up and be persistent. USU (my number 1 choice last year, didn't even talk to me after applying year 1.) and didn't offer me a slot until April 10th, after another candidate failed to physically qualify. Don't be afraid to not dwell on last year unless you have made great strides personally... in which case draw attention to those changes.
Mark