Fix Alerting on Expired/Rejected Web Sessions

I discovered that alerting on Expired/Rejected sessions is not being done correctly. These are both increasing counter metrics. Therefore the current threshold conditions will fire when the accumulated values exceed the threshold value (currently set to 15). But this is wrong, we want to alert on high rates of rejected or expired sessions. I assume the value of 15 meant 15 per-minute, but I'm not really sure. So, anyone with an opinion of what the correct value should be, please let me know.