A wifi serial port passthrough problem

[Zxc123456]

hi:
Testing environment:
1、STM32F407 connect serial port to ESP32-WROOM-32D.
2、ESP32 connect router into AT pass-through mode.
3、Set up tcp/ip server.
4、Repeated data sending and receiving.
Result:
1、When the serial port baud rate at 115200.The speed only 11KB/s.
2、When the serial port baud rate at 921600.The speed only 40KB/s.
2、Need 30ms-150ms can complete a send and receive cycle.
Question:
1、Can improve transmission speed? We need used to transmit video and images.
2、If it is only using serial connection can be achieved 300KB/s.
3、If not reach the speed. Does it need to be replaced with spi or sdio to connect.