There is a better way, but not exactly one step: Put all templates files in a local directory, where you could always access easily, then open the template file of choice from there.
Export from LibreOffice
The following steps are required to do only once. Preferably using LibreOffice 5.3 or newer, as some information may not be applicable to older releases of LibreOffice.
Open LibreOffice (or run libreoffice from Terminal or the application launcher).
In the sidebar, click Templates > Manage Templates. The "Template" window will appear.
Select the first template, then press Ctrl+A to select all templates (Notice that selecting none or all will disable the open button).

Click Export button. The "Select Path" dialog will appear.
In the file dialog, select a directory of choice and click OK to confirm. All templates will be exported (copied) to there, then a small dialog will appear when successfully exported.

- Close all windows of LibreOffice to finish. Then, open target directory i.e.
~/Documents/exported in File Manager to confirm that all template files were exported.

As a result, you will have all template files (with file extension *.otp,*.ott) in the directory of choice. For LibreOffice 5.3 that was installed manually, there are 21 template files in total.
With template copies: Two steps
Since all templates have been exported (or copied), user is now able to open template files, without having to open LibreOffice at first anymore. This approach has two steps.
Open target directory i.e. ~/Documents/exported in File Manager.
Double-click the template file of choice.
This approach is good enough for most end users.
With desktop shortcut: One step
To reduce another step, create a shortcut to the desired template file to open it directly from the desktop. This approach has only one step.
- Double-click the shortcut without having to open File Manager.
Productivity trap: Creating too many shortcuts on the desktop will clutter the desktop and user will be less productive. I'd suggest one for the local directory where all the templates were exported, and another one for the most used template file. The fewer, the better.
Additional notes
Older releases of LibreOffice are more tedious to export templates via GUI, due to the user interface is less accessible to browse and select the templates. Also, the keyboard shortcut to select all templates doesn't work.
In that case, it is faster to copy recursively from the source directory of template files via Terminal. The location may differ, depending on how LibreOffice was installed.
If LibreOffice was installed from the repository, template files are found in /usr/lib/libreoffice/share/template/common/ directory.
If LibreOffice was installed manually using DEB files provided by the official website, template files are found in /opt/[libreofficeX.Y]/share/template/common/ directory.
However, copying the template files from source directory has one disadvantage: some template files may be provided elsewhere. For example, MediaWiki publisher extension provides mediawiki.ott that is found in ../share/extensions/.. instead of above locations.
Tested using LibreOffice 5.3 in Xubuntu 14.04; LibreOffice 5.1 in Xubuntu 16.04.