That's a hell of a lot of repetitions for a new exercise with weights that are too heavy. An endurance exercise shouldn't start out uncomfortable. It sounds like you already have a pretty good idea about whether this is reasonable, but are being pushed to ignore your instincts and your body's feedback. I'm not an expert, but that sounds like way too much. When people exclaim about how sore they are like they're happy about it, they're not playing it up. It really ought to feel good.