I run 39x15, which gives about 69 gear inches. I average between 16-20mph. I am definitely a spinner, so 39x15 might be too spin-happy for you, but I would still recommend you try a lower gear. Either with the 17 like you said, or maybe try 42x15 if you happen to have a 42 tooth laying around. That gives you 75 gear inches, which would be a drastic change from what you have, and require some getting used to, but might work out well.