Lag with 3 accounts after hearthing

[WOWBOX40]

try typing this into all characters chat then /reload and then hearth normally.
/console worldPreloadNonCritical 0

There's something else going on though, you should be able to hearth 10 characters at once on that system easily.

His cpu has 4 cores / 8 threads and he plays with 4k on max settings.