Sorry, I didn't realise you were looking for sugar coated feedback. If 15 levels isn't enough to hook your customer into paying a few bucks, then you're doing it wrong.
If you still think giving away 100 levels made any logical sense, then I won't waste time trying to help you out with clear cut advice based on 3 years of app store experience.
We're indeed just treating this as a useful experiment. Games are just hard to compete in. We're not committed yet to staying in games, and hopefully the design/monetization/marketing lessons will give us a significant edge in smaller niches where the competition seems much less savvy, at least for now.