Nah this would be too much for the HCs to handle and it would be difficult and maybe lag the server because then the game would get confused if the person that was frozen left but think he/she was still there. But this is what i think, you gotta hear it from a staff member on the lava server
Some of these seem to be made up at best.
HC's to handle? HC's don't do all the freezing, nor is this much more handling to be done. Lag the server? Does freeze lag the server? And if the person was there or not would have no change if this effect was added.
Granted, I deleted two of your reasons that were reasonable so I could respond to these.
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Now to the suggestion. 15 minutes sounds much too long. 5 might be better. And it has to be so you can unfreeze them manually either way. Otherwise, decent suggestion.