It's all about the connection speed and the size of the file you want to commit. If you have a slow connection, try fixing when no one but svn is using the internet. This can help svn use the full bandwidth of your internet connection.
In the end, if you have the same problem, you should update your custom-httpd.conf file on your VisualSVN server, for example, the following code:
Timeout 300000 KeepAlive On MaxKeepAliveRequests 0 KeepAliveTimeout 500000
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