first thing you should do is enable the gzip compression in your server or hosting, the 15kb text files after compression is really small.

inline or not inline is depends on how you manage your website. You don't really need to fine tune every page to do not contain un-used css. Just imagine if you have 10,000 page to manage. Sometimes inline css is slightly faster as no second request is required.

As the matter of speed, Google do say that page speed will affect ranking but the weight is, if your content is better than your competitor, slightly slower is okay. Therefore, if seo is important to you focus on contents instead of managing css files.\

just my 2 cents.

First thing you should do is enable the gzip compression in your server or hosting, the 15kb text files after compression is really small.

Inline or not inline is depends on how you manage your website. You don't really need to fine tune every page to do not contain un-used CSS. Just imagine if you have 10,000 page to manage. Sometimes inline CSS is slightly faster as no second request is required.

As the matter of speed, Google do say that page speed will affect ranking but the weight is, if your content is better than your competitor, slightly slower is okay. Therefore, if SEO is important to you focus on contents instead of managing CSS files.