It will depend on where your keywords are place in search results. If it's lower than page 2 It will be difficult to achieve it within that timeframe. You can try and push some links from an automatic link building platform for some related keywords so they synergize between them, but make sure they're quality ones and with text around it.

You can also do allot of guest blogging on as many different dofollow blogs as you can. Just make sure they are blogs with a high domain authority.

Within 15 to 20 days its not possible but you can try to get backlinks for those keywords from high domain authority to improve your keyword ranking.

Hi friend, if you are doing organic SEO it will take minimum 3 months to bring your keywords to top. If you need to bring your keyword to top within no time it would be better to do PPC. I dont know how long you had been doing SEO for that keywords. Better you change your onpage details like title tag, description after doing all he changes go to web master tool and fetch it.

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I wouldn't say it's impossible to get those keywords to the top since you're already ranking for them in that timeframe, unless of course they are very competitive.

Buy some blog network backlinks and you will be on track to achieving your goal. However, it's likely to take much longer than you expect because it's harder to rank sites now than it was 2 years ago.

If you don't know seo , then the best way would be to outsource or buy links.