My “Help > About LibreOffice” box shows the following:
Build ID: 1:5.1.1~rc2-0ubuntu1~trusty0
CPU Threads: 4; OS Version: Linux 3.19; UI Render: default;
Locale: en-US (en_US.UTF-8)
The “File > Templates > Manage” menu in Writer displays the Form Controls tool bar rather than the Template Manager, although the shortcut key combination referenced (Shift+Ctrl+N) displays the Template Manager properly. Bug 92067 says the FontWork toolbar was displayed in the same circumstance, but was “fixed.”
I’ve gotten away from using Writer regularly as it isn’t suitable for much of the writing I do, but I’ve tried to keep it updated as it does have a lot of features that work. I can’t therefore say with any confidence when this Template Manager bug first appeared, since I’m not sure when I last used the template manager anyway.
This might possibly be related to Bug 59427 as well as 92067 ...
The template menu item in bug 92067 was fixed from v5.2.0 and 5.1.2. You seems to have an older version, so you might wanna try if a newer version fixes the problem.
*** This bug has been marked as a duplicate of bug 92067 ***