Can one really 'lose' old bad grades and get a fresh start? 15 years ago I was young and dumb, now I'm not as young. No way around it, I did poor in college. My grades were abysmal and were part of a period of my life that has long since passed. I'm now at a point in my life where I'd love to go back to school and earn the degree I never did, but I've got my past mistakes looming over me. 

Even if I start in a community college and get a perfect 4.0 for everything I'm enrolled in, my previous transcript will bring down my average. Completing a bachelor's is going to be far more of an uphill battle than it would be even just for an adult going to college while juggling a full time career and family. Is there any process to either ignore college work after a certain number of years have passed or a method to have them expunged?
That's not necessarily the impediment you may think.  The institution where I taught would not accept nor transfer credit over ten years old.  Pick one or two colleges you might attend, visit their admissions offices, and ask.  There's a good chance you can start fresh.

There are two things to keep in mind.  Your transcript from your old institution will still be there, and you will be asked for it when you apply for any degree program.  It may lessen your chances of admission, but probably not because fifteen years is a long time.

The other is that you should be honest about your education history on your resume.  Once again, fifteen years is a long time.  Do well now and no employer will even consider that ancient history.

Go for it!