I haven't done STP in over 10 yrs, but when I did do it there were lots of pacelines. You should be able to find a group traveling at that rate - some groups will be traveling faster. When I did the ride, no one seemed to mind if you participated in their paceline as long as you knew what you were doing and took your turn at the front. I'd ask politely before you jump into a paceline. Maybe you could ask around at the staging grounds at the start of the ride to try and find a group that wants to ride at your pace?

Drafting will make the ride easier. If you train well, a 14 mph average should be an easy pace. I've met people who've done the whole thing in a day at a 20 mph pace, but they were pretty serious riders.