Checkout slow without proxy

Hello,

we are using heavily "svn:externals" on our repositories.
A full checkout of a typical repository takes 20 Minutes. If I configure a HTTP-Proxy in my subversion-client it takes only 13 Minutes...

We are accessing our repository over an apache via https - due to the https-Connection no cache-hits should occour.
How is it possible that a connection over a additional station is faster than a direct connection?
I see also connections in "FIN_WAIT2"-State on the Server - can they slow down the checkout of the next external?

We are using Subversion 1.5.1 on Apache 2.2 on the server-side (the Subversion-Server is not public availabe).
I've tested with a Subversion-Client 1.7.1.

Thanks in advance.

Rgds.
Dieter

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