error on number of post display (view infinity) solution

I need view only 15 post in a page, but i have eg. 50 post in category.
then for view only 15 post I need pot this code: posts_per_archive_page=15

then what is the error?
the error is in this code:

[archivist template="ultimi_video" category="mypostcategory" query="post_type=episodi&post_status=publish&orderby=date&order=DESC&posts_per_archive_page=15"]

whit this code, I don’t see only 15 post, but 50! (infinity post).

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SOLUTION: the error is on the use of this codecategory="mypostcategory" the category is need impost in “query” code with number and not out the query line.

eg: (mypostcategory -> 38 )

[archivist template="ultimi_video"  query="cat=38&post_type=episodi&post_status=publish&orderby=date&order=DESC&posts_per_archive_page=15]

with this code the problem was resolved.

http://wordpress.org/extend/plugins/archivist-custom-archive-templates/