You can increase the speed of OpenVPN connections by increasing the size of buffers in the config.
So, briefly, the buffer size is a value that indicates the maximum amount of data that will be transmitted per unit of time. It so happened that in OpenVPN this parameter is 64KB. At the same time, the number of sent packets per unit of time is limited by the rate of passage of these same packets. Accordingly, the lower we have the packet passing speed (the more ping will be), the lower the speed of OpenVPN we will receive.