First time on a bike in 20 years and I did 15 miles!

[Owlie]

Welcome to TE! 15 miles?! Holy cow. My first ride was probably 2 miles...

Anyway, to answer your questions...There's sort of a continuum between flat-bar road bikes and hybrids. There are some that are essentially a road bike frame with flat handle bars, and there are some that fall closer to the mountain-bike end of the spectrum. Trek has the FX series, which actually seems to encompass a lot of that spectrum, depending on which particular model you look at.

Get what fits you. Test out a whole bunch of bikes. The rental program that the shop offers is nice because you can take it out on a longer ride. Once you've found something that feels good, you can have it properly fitted to you when you buy.

As for speed, well, you have options, even if you get something that's more "hybrid" and less "flat bar road bike", like changing the tires out for slicks. Riding more and pushing yourself will probably make for more speed, more so that whatever you're riding. Just my guess, though.

Edit: Depending on your proportions (short torso? long femurs?), Cannondale may not be the best company to go with. IME, they tend to have longer top tubes. Take a look at Specialized.