If you put 15,000 pages online at one time you can guarantee Google will see it as spam and never give much benefit.
I would recommend interlinking. So if on one of your pages you are talking about "red flowers" then link that to another one of your pages related to red flowers, then if image is "blue flowers" link to another related page on your website. Interlinking with lots of pages on your own website is VERY POWERFUL and can pretty much outrank almost 95% of websites.
do a sitemap and get lots of deeplinks "pr links"about a pr7 will assist you in getting a good crawl, i would advice that you point your highest PR link to our sitemap