Y Axis not moving fast. (no replies)

Good day All!

Into: I am using RAMBo v1.3 with Marlin FW 1.1.9 on my 3D printer.

Configuration :
My 3D printer is made out of aluminum extrusion and has a large print bed.
Travel limit for X is 500 mm, Y is 500mm, Z is 200mm.
The motors are all NEMA 23 motors.
I have 1 motor on X Axis, 2 motors on Y Axis, 2 motors on Z axis.
X and Y Axis is belt configuration. Z is on ballscrew.

On my Y Axis, I used the first Y motor, Y1, on the RAMBo Y Driver and second Y motor, Y2, on Extruder 1's driver, E1.
In the firmware, I enabled #define Y_DUAL_STEPPER_DRIVERS and set #define INVERT_Y2_VS_Y_DIR true

There is only 3 endstops - Xmin, Ymin, Zmin.

Problem:
The Y axis is slower than X Axis. I got the Y axis to travel a distance of 480 mm from 0 mm.

For X Axis, I can move the gantry fast at F15000 mm/m, but on my Y Axes (2 motors), they are moving at max F10000.

My feedrate; #define DEFAULT_MAX_FEEDRATE {250,250, 6, 250 }
#define DEFAULT_MAX_ACCELERATION { 800, 800, 100 , 1200 }
Jerk does not matter because this is at high speed from 0 mm to 480 mm.

I have gone through the Marlin 1.1.9 FW looking for anything related to feedrate, Dual motors.
Couldnt find anything.

Hence, do y'all know any idea? problems I am not aware?

Thanks in advance.