Depends, if increasing the current on 90 Kv makes it works, the the 75 Kv will work with a lower motor current, easing the load on the ESC, but there is a big chance that the motor is already saturating badly with the current needed to achieve decent performance with pneumatics, in this case changing the Kv won’t help, that’s is even ignoring the heat generated
This is experiment I recommend everyone to do, print a pulley that goes over the motor one and run a 1:1 gear ratio, preferably with smaller wheels
Even 190 Kv works wonderfully, if you an esc that can handles the current, don’t try that on the ones rates far less or it will overheat in no time because you need high currents to keep the performance with the higher Kv, but for the motor itself it makes no difference in torque capability or heat generation using a high Kv with higher current or a lower Kv with lower current