Had a couple of older PW 2.7 sites slow to the point of failure this week. A bit of digging revealed that the external image compression service used by ProcessImageMinimize is no longer available. Development on the module ceased some time ago.
Quick fix was to uninstall the module and edit the output code to use native PW image options. All affected sites operational again.
Next step is to update them to PW3.0+ ...