I was about 8 years behind on my logbook when I decided I had to do something. Took some others advice and got logbook pro. I brought forward all my time that I had logged on paper as a few separate entries. So all piston single engine went in on one line, same for multi, then turbo prop, then jet SIC. I started the detailed entries with all my turbine PIC, as it wasn't logged anywhere, just on trip printouts. To log that ~6000 hours took me probably two months of going at it pretty hard on my days off. In the three interviews I've had since that time, only one even looked at my logbook. For what its worth, they were impressed with the LBP printout. Its definitely much cleaner than a traditional written book.

Its going to take you forever to log 15000 hours in detail, maybe try to find some significant, logical break point like I did and go from there?