It is a lengthy project if you are looking to target premium keywords.
You have to read all the basic stuff and take special care on the OnPage side to balance out the 15 keywords on the site. And then do the normal Offpage stuff for each of them till you get the desired position for each keyword.
I don't know if you know this basic stuff or not. But if you don't know then you can read some threads here in this section which will help you out.
15 keywords is a little bit too many, you don't have to promote everything. just focus and target the keyword itself, including the keywords on the domain itself is another good practice it will lessen the keywords you need to promote btw.
too much of these i guess goes into the realm of spam.
to optimize a website for 15 keywords, you should separate and group related keywords and make a web page for each group and interlink where appropriate. for example, you might have 3 different keywords for 5 different pages. ranking well for 15 different keywords on a single page is a difficult task to accomplish to be sure.
You can make this:
Build your site
make a section for each keyword
build links for each section
in the index you do some stuff like list the sections and post part of some articles in it.
I suggest you focus first on just five keywords and work on the other keywords once you see good rankings already for the first 5 set.
You will need a lot of quality backlinks to make all of them rank. Build links in directories, forums, blogs, and other relevant sites for more positive results.
Will take some time, I would narrow it down to the keywords with weaker competition to start and work on those and once you get them up ok, move to the harder ones.
Try to rank your key words then write your content incorporating your keywords. Emphasize the first ones on your list in the title, write your content so it doesn't seem like you are being repetitive.
Readable content is better than keyword stuffed content.
Well optimizing 15 keywords for single page is really hard. I think the best way if use different pages or sections on same site for each keyword. That would give you faster result.
15 is no problem if they are organized into different sections. I have some sites with a couple of main keywords common to all pages and then over 30 specific keywords targeted for different section.
