You're probably going to want to submit this to our support team so we can ask some questions regarding your hosting provider, configuration and setup, and possibly gain access to the site to take a look. Depending on what's going on we may also need to get some information from your and/or your host from the server event logs. It could also be related to the hosting environment. If you're on a shared server with multiple sites running then executing a web service call for 15k products may only go through depending on the traffic to the other sites...not just yours. You should also provide the support team with your full 4 digit version number as there were changes in the feed execution from 8.0.0.0 to 8.0.1.2.
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