I have a template that I created by copying a long-running doc (Doc A) and ripping out many unused pieces. The resultant template (Doc B) is pretty simple, 3 base tables, 2 views, 1 button and 1 rule. The tables are all empty and they have only a handful of columns, at most. There are only 73 words and 0 media.
I even tried creating a copy of the template Doc B before creating the template from the copy (Doc C), however when I create the template from Doc C and try to insert it into another doc (Doc D), a popup warns me that the template is over 2mb and it may have performance problems.
When I view the statistics of Doc C, it reports only the simple statistics I mentioned, but it does show version as 162, which is the same as the original complicated source document. When I view the history of this document, it says it is the first version.
It appears that somehow the template is either directly including the full history of the source doc or has a bug in calculating its size.