I'm crazy for a woman 15 years younger than me. Can a woman even imagine having sex with a guy that much older than her or am I dreaming?

That all depends on whether she’s crazy for you! People do tend to match up with others of a similar age, but they don’t have to. Plenty of people, men in particular, have partners who are much younger than themselves. Picasso did it, Murdoch’s doing it; among less famous people, one of my best friends has been married to a man 14 years older than her for twelve years. Age is only an issue if you make it one. If you’ve got all the other things that attract people to each other - personality, interests, etc, and there’s also physical attraction, then go for it!