PPTP VPN quality

I have a question about PPTP VPN over NAT. After installing OpenWrt (after stock firmware) on my TpLink Archer-c7-v2 I had a problems with PPTP VPN over NAT. After reading https://openwrt.org/docs/guide-user/services/vpn/pptp/nat_traversal I get it working but experience is a lot worse than on stock firmware. Connection to services (SQL Server) are lot slower or timeout. Is there anything I can do to fix this?