e-Newsletter plugin breaks / stalls after sending a newsletter to 15,000 subs

I click on the eNewsletter link on the sidebar and it just stalls and stalls. Ive waiting 45minutes once and nothing. I don't think this plugin can handle sending to 15000 subscribers. Ive downloaded a plugin that lets me see the active crons and its not in the list.

I thought it would be a cron still running but no.

I can get to the settings page but it seems every page that might have to do with the subscription list or reports puts a HUGE memory strain on the plugin.

How can I diagnose this?

Cheers.

Ian