It might be worthwhile to raise the price significantly. The apparent discount from $15 to $9 makes the service look less valuable and the company less successful. A class of desirable customers are those willing pay hundreds of dollars a month or more. For serious work, the cost of integrating with a service is high and the long term financial stability of the service is important. Low prices correlate with higher risk that the service will disappear.
I believe ImageOptim is older than Optimage but they seem to work the same way.
They also offer a paid web API service with a similar price [2].
Posting just as an alternative, the more the better.
[1] https://imageoptim.com/mac
[2] https://imageoptim.com/api/pricing