Slow Internet when using Firewall

[Guest]

[Alexw]

Hello,

I tryd alot of Firewalls to secure my VMWare ESXi 4.1 server.
But the most of them just slow my internet alot. But for now Edian allowed more speed then the rest of firewalls.

I got a 100Mbit up and down connection but all i get is 15Mbit up and 25Mbit down.
When i try to do a speedtest again without any firewall i get 85Mbit down and 65Mbit up.
(Used SpeedTest.net)

So can you see my problem?
My specs are the followed:

Intel Pentium 4 3.4Ghz
Assigned memory: 512MB
Assigned HDD: 8GB

Any solutions for my problem?

Thanks in advanced,
Alexw