We have many deployments with camera lengths way beyond 15m. HDMI cables can be iffy over these distances and expensive, but we successfully utilise Cat5 --> HDMI convertors to achieve the required distance (specifically ones from Extron (although I don't have an exact model at the moment) - we have had difficulties with other manufacturers). If you want to look for good quality cables, check out "Blue Jeans HDMI cables" (google) -
Yes, this will be beyond Cisco's support, but if you need achieve the distance, you have to do something - right?. If the second camera fails, the first thing to do is temporarily bring in back within spec to see if there is a issue in the normal configuration.