Forum Moderators: phranque
If your box is co-located in a facility that has a direct fiber-optic backbone connection, then the problem may be with the applications you're hosting -- Are you using a CMS with a huge database? If so, is the DB query code optimized or just something that someone hacked-out over a weekend?
Or maybe the site's coded in PHP, but not very well coded in PHP...
Out-of-the-box with the Apache-supplied config files, you should not have a problem hosting a 'typical' site with only 15 users --or even 1500 users-- on an un-shared high-end machine. But the nature of this site and it's users, and how they might differ from 'typical' is not at all clear.
Apache provides several tutorials for configuring Apache servers, and there are hundreds to be found using search engines.
Jim