These displays use the SPI bus for touch information which is typically limiting the speed. Further more the touch is not capacitive but resistive which means the display needs some physical pressure to detect a touch. So I think the possibilities to speed up touch are pretty limited. At least with a justifiable effort.
What you could try is upping the speed value (which sets the speed of the SPI bus) in the line you added to userconfig.txt:
According to this readme the default speed is 2MHz and the value used is 50kHz. The lower value is taken from the config-5.txt file of Waveshare. This does not mean higher values won’t work but I have no experience with that and can’t predict the effects of a higher value.
P.S. The “xohms” value you see in the dtoverlay line controls the sensivity of the touchpanel. So you may play with that value, too, to improve responsiveness.
P.P.S. Do you have any other hardware connected that possibly uses the Raspberry’s pin 22 (GPIO25)? This might interfere with the touch panel which also uses this pin to detect / signal touches (