Httpd – Add Subversion to XAMPP Apache install

In Http.conf file;

1 - You need to load fast_cgi module LoadModule fcgid_module modules/mod_fcgid.dll

2 - add this :

     <IfModule mod_fcgid.c>  
AddHandler fcgid-script .fcgi .php  
# Where to look for the php.ini file?  
FcgidInitialEnv PHPRC        "c:/xampp/php"  
# Set PHP_FCGI_MAX_REQUESTS to greater than or equal to FcgidMaxRequestsPerProcess  
# to prevent php-cgi process from exiting before all requests completed  
FcgidInitialEnv PHP_FCGI_MAX_REQUESTS      1000  
# Maximum requests a process should handle before it is terminated  
FcgidMaxRequestsPerProcess       1000  
# Maximum number of PHP processes  
FcgidMaxProcesses             15  
# Number of seconds of idle time before a php-cgi process is terminated  
FcgidIOTimeout             120  
FcgidIdleTimeout                120  
#Path to php-cgi  
FcgidWrapper "c:/xampp/php/php-cgi.exe" .php  
# Define the MIME-Type for ".php" files  
AddType application/x-httpd-php .php  
</IfModule> 

3 - make sure you give permission to your root directory to run CGI Options Indexes FollowSymLinks ExecCGI

For a good information you may visit here.

From Apache 2.2.15 Changelog there is memory leaks fix in 2.2.15 but if you top output is after apache start it's really huge from my point of view.
Did you try a worker config ?
Could you add the output of ldd tool on you httpd binary ?