10%-15% is a great range , beats most things in the physical world hands down.
IMO the lowest a POS rate could go is 5%, anything below that and you are better off with utility stocks that pay out ~5%.
Depending on how many days you set to hold the coin before it receives a POS reward, some people that do more trading , usually will not keep the coins long enough to gain the interest, so whatever rates you do decide on, your actual rate for the year will always be a little lower.
P.S.
Glad it worked out for You & PalmDetroit.