I have Apple Music free with my Verizon phone plan. Can I upgrade to family sharing? Will it cost me 14.99 or the 5.00 difference?

You may want to check with Verizon. They don't offer a Family subscription to Apple Music but if all of your family's lines are with an eligible Verizon plan, a free individual plan for each member appears to be the way as the following mentions signing up lines. https://www.verizonwireless.com/support/apple-music-faqs/