I'm not sure why the listing agent would be telling you what the commission on the sale would be.
But the answer to your question is, sure you can try to negotiate a lower commission. The commission is an agreement between the seller and the listing agent/agency. But some listing agents will negotiate their side of the commission, if/when they determine that there is no "buyer's side" commission to be paid.
In fact, some listing agents have already put it in their listing contracts that if there is no buyer's representation, the seller will save 1-2% in commission. In that case, the seller will have to determine if s/he wants to pass that savings on to you.
But it's worth a try.