Since I only wanted to charge my Evercoss Android One rather than having my phone content exposed to company hardware, I disabled “Media device (MTP)” USB mode there. This is actually easy since there is a shortcut in the notifications which let’s you do just that.
The tricky part is to turn that back on when you are back home and want to connect your Lollipop phone to your private computer. The system won’t find the phone unless “USB computer connection” on your Android is either set to “Media device (MTP)” or “Camera (PTP)”. The notifiction which used to be there in MTP mode is gone so there is no shortcut to get back to that setting.
After looking for that setting for ages, going through every possible menu and exploring the deeps of Android 5.1.1 was about to give up when I finally found the menu I was looking for, well hidden as a tiny “more options” button within the “Storage” overview screen.
Touching that will finally bring you to the “USB computer connection” settings where you can choose either one of the available options to make your phone visible to your computer again.