ROV speed control issue

Hi, I am studying in a university, invent ROV with Pixhawk1(ArduSub V4.1.0), QGroundControl(latest version).
Thrusters are like the following picture.

I am using APISQUEEN U92 and ESCs for 1‐4thrustes to get large thrust.(APISQUEEN U92 underwater thruster, for kayaks, paddle boards, surfboards, inflatable boats, ROV etc. – Underwater Thruster)

However the ROV moves forward very slowly compared with sideways and turning.
Could you please tell me any idea to change some parameters in QGC or Mission planner.

Thank you