due to keywords if a keywords like How to optimize your website in 15 days then i think no problem but if keywords like "optimize website" then some difficult
if the competition is extremely low, you can optimize a page for a random long-tail no one is looking even in less than 24 hours.. Like, if I want to rank a page for "why do idiosyncratic people ask weird questions", I could do it fairly quickly with a WordPress or a Blogspot blog. otherwise, 15 days is a really short term for any SEO project, perhaps it's only good for an SEO combat or something.
Its complete depends on the 'keywords" what you select and the website on which you are targeting the keywords. SEO is not a magic to get ranked for the desired keywords on the 1st page on google in very short period of time frame.
It can be only if your website is facing least competition. Only in that case there is a little possibility of ranking up that fast.
If you're targeting long tail keywords then it's easy to optimize with wordpress but it's totally different with other short keywords