Working FPBX 14 distro, fully updated. Module updates worked, system updates worked, yum worked, ping mirror1 and mirror2.freepbx.org worked, with good ping times (~50ms). AT&T Gigabit Fiber internet.
Tried to upgrade via 14->15 upgrade module a few times over 48 hours (Thu/Fri this week) - would always fail the precheck with a curl timeout.
Seemed to be similar to what is described in FREEPBX-20726 (https://issues.freepbx.org/browse/FREEPBX-20726). I changed the following line in Versionupgrade.class.php:
And the upgrade precheck ran successfully, and then the upgrade went on to complete fine.
Sharing here in case anyone else gets bitten by this issue …