You are not employed to give out pricing. That can be done with a simple webpage.
You are there to help the buyer understand if their budget, fits with your product and if your product solves a big enough pain to warrant spending their budget with you.
First, if the buyer interrupts you… stop the demo/conversation right away. You’re wasting everyone’s time otherwise.
If the competitor is offering everything you do for 15% less then ask “I understand that price is important. Can you let me know what the budget is that you’re working to and I’ll see if that 15% is accurate?”
“I can share the pricing, that’s no problem. Can I ask a few questions to see what tier of service you require first?”
If the buyer still doesn’t budge though… just give them the pricing and move on. They may be pricing you against the competition… the may be ready to do a deal but they’re shit at negotiating and they’re trying to get a discount.