How to disable iTunes 12 on Windows 7/10 startup

This was driving me nuts. Finally found a solution here: http://superuser.com/questions/948157/itunes-starts-automatically-at-startup-on- windows-10

Seems to be a problem related to iTunes in combination of other media programs like Plex Media Server or others.
First try what has been suggested above (normal windows startup stuff, sync issues or bluetooth). If none ot that helps this might.

in iTunes 12.2 - check Preferences > Advanced and set the option Share iTunes Library XML with other applications
Check that box and restart the computer. Worked for me.