I have a 75V 300A Original VESC, recently I have tested it with a 5kW motor to its peak current of 100A at 48V for about 2 hours, where I noticed there is a instant rise in temperature of the mosfets and they stayed between 85C to 92C even with proper heat sink and a fan for cooling. I thought of testing the same hardware with 10kW and 15kW motor rated for 48V. my concern with the hardware is will it be able to withstand them 200A and 300A continuous for at least about 2 hours minimum. If Im not wrong 75V 300A VESC uses irf7759 160A Id and 75V Vds mosfet of three in parallel, which peak is 480A should able to withstand 300A continuous.
You will need to have a more substantial cooling setup for this long running, I would suggest using some old pc heatsinks as they can dissipate a lot of power and are very cheap used.