Which length and model Abus Steel-O-Chain do you have? I thought they all weighed a lot more than 1.5 pounds. Looking at their web page it looks like the lightest one weighs over 3.5 pounds and the biggest/heaviest over 8 pounds. Is there another model that is lighter that I am missing?

I use a cable lock that weighs a bit under a pound. When there are two of us we share one lock. I tend to tour in the US, mostly in small towns or rural areas where theft is not a huge concern.. In tiny towns that are many miles from the next town I usually don't even bother to lock. In larger more "bike friendly" cities I am super careful where I leave my bike, locked or not.

Carrying a heavier lock is something I have not even considered and probably will not unless my preference for small town touring changes. Sometimes I even consider leaving the little cable lock home, but I have not actually done so.