Sometimes, you’re unable to save a list that contains a lot of data as a template.
Below, I’ll show you step–step how to save a template with 16,000 list items.

1.      Go to List Information and click on Save list as template:

2. Type File name, template name, and
template description then check Include
Content check box and click OK
button.

3.      Your site will generate an error message
as shown below:

4.      Go to Central Admin and navigate to Central
Administration, then click Application
Management, Web Applications,
and then select General Settings:

5.      Change the Maximum Upload Size default setting to 1024MB then click OK.

6.      Save list as template again.