Just be glad you can even contemplate setting PR's without total absurdity. Who knows what you could do if you lost 15 lbs. (Hint, hint.)
It does help that I was never a runner, and hence never had any results, until I was in my 40's. Thus the period of deteriation from my established standards has been much shorter than for those of you who have a running background. I do think it rather unlikely that I will ever surpass the 2 PR's that I recorded in the Needham TF's because they were set several years ago under ideal conditions. However, my PR's on many of my more occasional runs were not especially extraordinary, and as such, still appear potentially accessible. It also helps that they have rerouted the trails in Powisett (where another couple of meaningful PR's were set) so I need not even consider comparing my current standards of performance with yesteryear.
Regarding losing 15 lbs, that still seems like a relatively tall task, although I did get as low as 173 (from about 205) when I first started running in 1999. I'm not sure my body type will ever conform to a classic runner's build. Even though my weekly mileage is way up from anything I have ever done in the past, I seem to be stuck right about 184 lbs. Maybe I should schedule a few more stressful overnights to help the cause.