Kryptonite New York Lock + Chain

10.80 lbs with a 3.25' chain.
15.25 lbs with a 5' chain.

I presume the OP was exaggerating.... slightly... but one can easily add a few pounds of precious weight with a lock. The more secure, the heavier.

Eons ago, my father had gotten some conveyor chain, about 1.25" x 1.25", thick, and heavy, covered it with an inner tube, and locked it with as big of a lock as he could get at the time. It would have taken a little while to hack through. But, he left it locked to the rack where he would park his bike for commuting.