Q: Showing slideshow from your computer on someone else's TV.

It's impossible to answer without knowing what the facilities at the venue are.

Does your Mac have a HDMI port? Purchase a HDMI cable. Otherwise there will be no sound.

BTW there really is no such thing as a "standard PC Video cable'. I strongly urge you to go visit the venue and see the TV for yourself. A lot of folks find themselves at events like this lost as the venue are clueless and they're not very knowledgeable either. Simply you have to go look.