The default libinput touchpad driver installed in recent versions of Ubuntu does not have an option to adjust the two-finger scrolling speed. You can see that from the output of xinput --list-props <id> where <id> is the device ID of your touchpad as obtained from xinput list.
However, with the HP Probook 450 G1 you are lucky as a Google search seems to indicate that it has a Synaptics touchpad. For this, an alternative driver is available with more options.
Install the Synaptics driver as follows and it should already work (source):
sudo apt install xserver-xorg-input-synaptics
If it does not work yet, also follow these instructions to override the libinput touchpad driver explicitly.
Configure the option Synaptics Scrolling Distance with a command like the one below. <id> is the device ID of your touchpad as obtained from xinput list, and you have to play with the values for the vertical and horizontal scrolling distance at the end of the line to find the right ones for you. If you use negative values it will give you inverted / natural scrolling.
Best Answer