Hello.
Reloading 2.6 works in-place. Some of the changes you may have made in 3.15 beta 2 may not carry "back", but everything should work.
As for the delay in starting the alert, this probably has to do with the settings on the alert. If your alert settings require looking at more than one sample, then it may take multiple samples for the alert to fire. For best results if you want your .wav file to fire on each lost packet, set "Samples to Examine" to 1, and Alert when "1" or more samples are over your threshold.
Another possibility for the delay is that PingPlotter waits for a period of time for a timeout. If you unplug a network cable and PingPlotter is set to wait for 10 seconds (9999ms, the default) before it sees a timeout, then the alert won't go off immediately when you unplug the network cable - you'll have to wait for the timeout period to elapse. You can change this in Edit -> Options, Packet. "Timeout Speed". 1000 or 1500 usually works pretty well unless you're expecting long response times as normal.
There is a bug in the 3.15 beta 2 release - alerts don't turn off right, and they are sometimes unreliable turning on. That will be fixed in the next build.
- Pete