Slow delivery despite seemingly correct settings

[Chris]

I have about 15,000 subscribers. It takes about 8-10 hours to finish a newsletter run, regardless of my per hour delivery settings (5000, 10000, 30000). I have a reasonably powerful VPS (currently configured with 4 CPU cores and 8GB RAM). I am using Mandrill for sending, with the Mandrill extension as part of Newsletter Premium.

The plugin says my cron system is enabled/working, and my max_execution_time is set to 0, which the diagnostics screen on Newsletter also acknowledges. With debug logging enabled, the only entries of note are at the start and end of each delivery engine cycle. At the start:

19-11-2015 13:09:30 – DEBUG – 14.0 MB – limits_exceeded> Setting the limits for the first time
19-11-2015 13:09:30 – INFO – 14.0 MB – limits_exceeded> Max time set to 285
19-11-2015 13:09:30 – DEBUG – 14.0 MB – limits_exceeded> Max number of emails can send: 2500

And at the end:

19-11-2015 13:14:16 – INFO – 28.0 MB – limits_exceeded> Max execution time limit reached

This last message is confusing to me given my execution time is set to 0. What else can I do to troubleshoot the slow delivery speed?

[Author]

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