Does anyone know of a good program that multiple people could enter in appointments that goes in 15 minute increments?

Phoneslips www.telexis.com works pretty good at that. You can choose to display appointment in 15, 30, or 60 minute increments.

It's also a replacement for those ubiquitous pink phone message slips (it's original purpose, hence it's name), plus a few other back-office tasks.

I used it for all of our office scheduling when I was a partner in a CPA firm. I still use it with just a secretary - mainly for the phone slips now.

--Peter