I used Scallion. Depending on the speed of your computer and the complexity of the .onion you want, it could be infeasible to create (taking years. You could get lucky, but highly improbable). I have a pretty nice graphics card and a relatively loose constraint (repeating characters)which sped up the process quite a bit, so good luck!
Its off topic but I’ll chip in. With 16 characters, you are just only getting 80 bit strong RSA keys as your HS name which is suspeced not to be good enough at this time. Using Scallion to insert easier words to remember in the address will only further weaken that margin and make spoofing your Hidden Service name well within the ability of those with serious computing power: NSA.