Are you hosting and playing the game on the same PC? If so, not ideal to do that with that hardware.
Bring it down to 1 server. If both servers are popular, choose the one with more popularity.
Install Windows 10 32-bit instead of 64-bit as you have just 2GB RAM. And stop every bit of unwanted processes and services as most of it is just garbage for everyday use. Once you stop it all, your idle RAM usage will come close to 500 MB and you will have a dedicated of at least 1GB RAM free for the HLDS usage. So keep checking the task manager.
Check your server internet connection and make sure you don't have any idle network usage whatsoever. Not even a single usage shown in task manager. And then check speed, if it's not even 2mbits/s UP and DOWN, just forget about hosting a 20 slot server. For more details, refer
here.
Are you sure that you can force a sv_maxrate "25000" as that much isn't supported by HLDS? None supported values fall back to default server values so that might be no use. Refer
this.
Meanwhile try these values;
sys_ticrate "1000"
sv_maxrate "20000"
sv_minrate "20000"
sv_maxupdaterate "100"
sv_minupdaterate "30"
Forcing a sys_ticrate might be bad, but as you are a server hoster, try tweaking it or remove it completely in case it goes unstable.
Don't run too much HLDS plugins, this involves all types of plugins which I can't even type here. So first try hosting a classic style server with least plugins and check how it performs.
Run a media player like VLC on the Windows background, but not sure if this actually works. Else just dump it because it's annoying.
Overclock your CPU if possible, "
do that at your own risk" and disable bullshit motherboard features that you don't really need. Check the airflow of your server PC, and temperature levels as it can cause the server performance to go haywire. Single core performance is really important for HLDS. Get a maximum clock DDR3 RAM stick if your motherboard supports it. Of course these solutions involve spending some money, if not forget about this.
Tried hard yet nothing? Try
ReHLDS and follow the above.
Also don't panic when you see some random high pingers, it's just their crappy internet, not the server's fault.