I would be very angry too!
Just go ahead and tell them to be gentle with your baby, or to leave her alone. Yorkies are so small boned, anything can happen. She probably gets hurt and thats why she's snapping. 15 weeks is still a tiny baby for a yorkie.
My friends know better than to tease or hurt my two, they know I would hit them!! Not joking!
Good luck with your problem, and come and vent anytime - we do understand
