To add to the above, Code 15 is triggered (at least on the 94~95 LT1) when the ECM detects CTS at -40F or lower for 2 seconds. On this application, that means CTS circuit at 100700 ohms or more (open circuit) for 2 seconds.

So if you're triggering Code 15, that means your CTS is intermittently reading essentially disconnected for 2 seconds or more. However, as Jim pointed out, it would be good to know what "temperature" is being reported for those times when Code 15 is not triggered as well. My bet is that it will read normal until Code 15 events happen, because the culprit is poor wiring causing a complete signal dropout.