Your comments

For me and I suspect 70% of free users, I'd be inclined to buy if one of these options were available: 


Offer either a free 14-day premium trial or a $5 3 month trial and then I'd feel the benefits and be hooked and pay the $15 anyway. 

Remove friction from the purchase would be a bonus by not asking for email up front, just display a page with the price range. 

Possibly the best and simplest option as you say you don't have many purchases, you could simply offer a 14-day free trial or paid with 14-day refund, maybe minus 20% for tax.

I would love to try before I buy, and I am sure I am not alone, you would certainly increase revenue if you can protect it.

Thanks for a great tool and keep up the good work :-)