Need answer here

In most cases, yes – although it does depend upon what plugins you are using and the load on the server generally.

it`s all about SEO plugins, btw are 15 plugins to much to handle?

Please see my answer above.

yes..how much plugins do you recommend so my site will not slow down when it is loaded?

There is no hard & fast answer to this! It depends upon what plugins you are using and your server’s performance generally.