Does anyone have an easy fix to stop Lightroom 2015 from re-populating endlessly upon opening on a Mac v. 10.11 running El Capitan? Lightroom does not respond and it is impossible to open the preference plane. The only choice is to Force Quit the program.
You can try and reset the Lightroom preferences back to default and check if that helps.
Press the shift + option keys immediately after you restart Lightroom, and select Reset Preferences from the resulting dialog box.
If what you mean by Re-Populating is LR opens automatically when you start up your Mac then that is caused by the LR app being in the Startup section of the system preferences or having the option checked to re-open programs that were left open on shutdown and or reboot.