How to adjust touchpad sensitivity on HP Spectre under Ubuntu 16.10

I can't find a way to decrease the sensitivity of the touchpad on my HP spectre laptop running ubuntu 16.10. Changing the settings in the built-in "mouse and touchpad" settings doesn't work at all - literally nothing happens when I change any setting under either mouse or touchpad.

I did some research and found out that I might need to adjust x.org settings just to change the touchpad settings (which seems absolutely ridiculous, btw, but whatever). So, I tried to learn about xinput.. but all the guides mention settings I can't find.. namely ones related to sensitivity or pointer speed.

For reference, here is the output of xinput --watch-props for my touchpad:

$ xinput --watch-props 15
Device 'SynPS/2 Synaptics TouchPad':
Device Enabled (139):   1
Coordinate Transformation Matrix (141): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
libinput Tapping Enabled (279): 1
libinput Tapping Enabled Default (280): 0
libinput Tapping Drag Enabled (281):    1
libinput Tapping Drag Enabled Default (282):    1
libinput Tapping Drag Lock Enabled (283):   0
libinput Tapping Drag Lock Enabled Default (284):   0
libinput Accel Speed (285): 1.000000
libinput Accel Speed Default (286): 0.000000
libinput Natural Scrolling Enabled (287):   0
libinput Natural Scrolling Enabled Default (288):   0
libinput Send Events Modes Available (259): 1, 1
libinput Send Events Mode Enabled (260):    0, 0
libinput Send Events Mode Enabled Default (261):    0, 0
libinput Left Handed Enabled (289): 0
libinput Left Handed Enabled Default (290): 0
libinput Scroll Methods Available (291):    1, 1, 0
libinput Scroll Method Enabled (292):   1, 0, 0
libinput Scroll Method Enabled Default (293):   1, 0, 0
libinput Click Methods Available (294): 1, 1
libinput Click Method Enabled (295):    1, 0
libinput Click Method Enabled Default (296):    1, 0
libinput Middle Emulation Enabled (297):    1
libinput Middle Emulation Enabled Default (298):    0
libinput Disable While Typing Enabled (299):    1
libinput Disable While Typing Enabled Default (300):    1
Device Node (262):  "/dev/input/event6"
Device Product ID (263):    2, 7
libinput Drag Lock Buttons (301):   <no items>
libinput Horizonal Scroll Enabled (264):    1

Am I destined to just have a horrible touchpad experience in ubuntu on this laptop? For whatever it's worth, the touchpad is so sensitive a tiny movement of less than an inch can move the cursor across the whole screen.

Here's the output of xset -q:

$ xset q
Keyboard Control:
  auto repeat:  on    key click percent:  0    LED mask:  00000000
  XKB indicators:
00: Caps Lock:   off    01: Num Lock:    off    02: Scroll Lock: off
03: Compose:     off    04: Kana:        off    05: Sleep:       off
06: Suspend:     off    07: Mute:        off    08: Misc:        off
09: Mail:        off    10: Charging:    off    11: Shift Lock:  off
12: Group 2:     off    13: Mouse Keys:  off
auto repeat delay:  500    repeat rate:  33
auto repeating keys:  00ffffffdffffbbf
                    fadfffefffedffff
                    9fffffffffffffff
                    fff7ffffffffffff
bell percent:  50    bell pitch:  400    bell duration:  100
Pointer Control:
  acceleration:  1/1    threshold:  6
Screen Saver:
  prefer blanking:  yes    allow exposures:  yes
  timeout:  0    cycle:  0
Colors:
  default colormap:  0x20    BlackPixel:  0x0    WhitePixel:  0xffffff
Font Path:
  /usr/share/fonts/X11/misc,/usr/share/fonts/X11/100dpi/:unscaled,/usr/share/fonts/X11/Type1,/usr/share/fonts/X11/100dpi,built-ins
DPMS (Energy Star):
  Standby: 0    Suspend: 0    Off: 0
  DPMS is Enabled
  Monitor is On