My warning sign was when I pulled out the postage scale to choose which parts to throw on my "climbing" bike build(Canyon Ultimate SLX.) The bike build was originally supposed to be a budget build, so I did limit myself from descending into full on weight-weenieism. Most of the components were stuff I already had laying around. I ended up at the 15lb mark...and that's with not sacrificing comfort for weight with things like the not-lightweight bars and seat. Also not the lightest groupset I could've spec'ed(mix of rim brake Ultegra 6800/8000.)
It's around 3lbs lighter than my "main" road bike, the only place that this difference is noticeable is on climbs. In reality, it's only a matter of seconds, but the perception is of liveliness and speed on the climbs. My racing disciplines lie off-road, so any performance benefit is almost meaningless, but I do enjoy the feeling of a "fast" bike.