I would say it is not about the 15% or whatever ROI you have, it is about actually have a customer that pays. These days because of places like google, facebook, and many other similar websites where you can use it for free, and they sell your data for marketing purposes, everyone is trying to build something that is free to use, and they will then make money from ads and so forth.

If you have a product, if people are willing to pay for it, then you are on the right track. Plus, how much you earn also depends on how much you spent, if you spent 10 million dollars, making 15% is not bad, if you spent 1000 dollars, making 15% is horrible. So it all comes down to how much you spend yearly, plus money on top of it to make it a sustainable business.