How to make NordVPN with DD-WRT Faster?

Router: Firmware: DD-WRT v24-sp2 (01/04/15) std. My current country: Latvia. Location of VPN server: Latvia.

I think NordVPN has better speeds than PrivateInteetAccess (PIA) in Latvia, but their manuals are worser than PIA's, for instance here a random collection of scripts and discussions. I am trying to speed up NordVPN coection here.

If I keep OpenVPN client on in DD-WRT (Services > VPN > OpenVPN Client > Start OpenVPN Client enabled/disabled), my inteet speed is 10x slower download/upload and ping is 20x slower although the VPN server is in the same city as I am. I used PIA too but it is much worser than NordVPN in Latvia (ping 4x worser; download 2x worser; upload 4x worser). However, some users have managed to get fast download/upload with their NordVPN and I am wondering how. I followed PIA's manual about VPN settings of DD-WRT here because they are much more mature than NordVPN's own ones. I substituted corresponding NordVPN's infos to appropriate places

DD-WRT settings

My settings in Services > VPN where the server is in Latvia

I have in Services > VPN; where I downloaded the certificates from here

• NordVPN single server of Latvia can be found by clicking Latvian flag here at the end; note, to found the correct IP can be confusing
• Encryption Cipher: AES-128 CBC but can be also AES-256 CBC
• TLS auth
• CA cert

In Services > Services

• DHCP Server > User Domain: LAN & WAN
• DNSMasq > Local DNS: Enabled

In Setup > Basic Setup > Network Address Server Settings (DHCP) [PIA DD-WRT manual]

In Setup > IPV6: Disable.

How can you make inteet coection faster with VPN?