if a people working in small IT company as a seo after 15 years what they will do means there is job security?

[Kim Cunnings]

It depends on how good you are as an SEO.
Same old tactics don't work that well (but I wouldn't say they don't work at all).
If you're flexible and willing to keep up with the changes in the SEO world, I'd say you are priceless!
There is barely such a thing as a secure job in this world anymore.
With economies crippling, industries changing, etc.
You need to adapt.
The only company you can vouch for is your own company.
The only brand you can be in control of is your personal brand.