Well I'm on my third bike in about 5 years: started with a comfort (slow, not comfortable, but got me falling in love with biking), moved up to a Trek FX5 (mine probably was a bit too big, but a great bike. I added bar ends to give me more positions on the handle bars, put fenders on in the winter. Changed to narrower tires (25s) and picked up a couple miles per hour. I will probably keep it for ever. I've ridden 70 miles on it and its got the triple chain ring and low gearing, so its a great climber (important because I'm not). Its a great bike, but ....... I wanted more, I wanted faster, longer rides. So, I moved up to a Specialized Ruby. Ruby Sue is wonderful. She fits me very well (Specialized sales people must have the most training when it comes to fitting you to a bike).
And I am really more comfortable for long rides. I'm not a whole lot faster than I am on the Trek now that I have narrower tires on it, but a mile or two per hour. Oh, and Ruby Sue is beautiful. That never hurts!

The fact that you rode 15 miles on your first (Your Rock by the Way) makes me think that you have much longer rides in your future and you may be road bike material right from the get go. They really are zippier, more comfortable and more responsive (at least in my incredibly inexperienced case). They look
hard to ride, but really are not at all. If I can ride one, anyone can!

But try a few styles out before you buy. What works for some, might not be what feels best for you.

Oh, and everything I've learned about biking, I learned right here. These ladies are awesome. Welcome to TE and have fun shopping!