My site was with primary keyword coupon codes, having 15,000 of pages

indexing by Google. But when i was generated my site-map i had 13,000 of

pages only.. what about rest of 2,000 pages?

You need to check your sitemap format. HTML sitemaps are for users. It seems that you are submitting XML or TXT sitemap.

That generally means that you have more than one URL pointing to the same page, e.g., http://www.yoursite.com/page1.php and http://www.yoursite.com/page1.php?print.

Alternatively, if it's a blog, or a directory, or a forum, Google may be indexing the category names.

Which tool could make a sitemap with so many pages?I just know xml-sitemap could creat a sitemap with 500 pages.
And you should to check whether some error in your pages.