You could use something like this the extension is made by RJ45 cable and not by USB. You might just make 15meters if you used a USB repeater though the first option might be the better one.

Thanks for posting that follow-up info Jack! I have all sorts of extenders and powered hubs kicking around here but like you say, they don't always work 100%. Every time I move a cam it seems like I spend an hour messing with cables and hubs looking for a combination that works without power or signal problems. Think I might just order some of those extenders you linked and see how they work out here.

I also had the same issue. Interestingly the cameras that worked best on a USB extension cable were the el-cheapo ones. The more expensive ones drew too much power. I finally settled on the USB Ethernet CAT5 extender combination. I had problems with a 20m Ethernet cable (but no problems with a 5m length which was really all I needed). I could (almost) get a cheap camera to work at the 20m limit, but the flicker was just too much to be viewable. The shorter length now means I've been able to upgrade my camera, giving a much better image quality.