Where can I find info on a Rohm RG-15 .22 cal. over/under barrel short derringer, made in Germany?

I came across this gun & I'm wondering what it's worth. I know it's really old. It still shoots. I tried to do searches online, but couldn't find the RG-15 model. If anyone can help out w/anymore info or a website I could go to, I'd appreciate it. Thanks!