You can't shorten a dissipator to 14.5". I think Randall posted a while back that 15.2" puts you flush with the FSB. That might shave 2oz off the end. Reprofiling is the bigger payoff to be sure.
Tell us more about your rifle...
What brand and profile of barrel?
What brand of forend?
What "other stuff"?
I have found that it can frequently be cheaper to sell your barrel and purchase a new one in the profile you want rather than having a major re-profiling done. JT Distributing is working on a pencil profile dissipator, so that might be an option.
But ultimately, fivepointoh is correct, and I would personally suggest that if you need a lightweight 14.5" carbine, then buy or build a lightweight 14.5" carbine. If you also need an accurate rifle with a longer free floated forend, then either stick with your Dissipator or build a Recon rifle.