Apparently, the Synaptics driver was replaced by libinput in Fedora 22, which doesn’t currently support kinetic/inertial scrolling. Here’s how to get it working.
Copy /usr/share/X11/xorg.conf.d/50-synaptics.conf to /etc/X11/xorg.conf.d/51-synaptics.conf, add the following to the bottom, and reboot:
Section "InputClass" Identifier "Enable kinetic scrolling for Elan Touchpad" MatchProduct "Elan Touchpad" MatchDriver "synaptics" Option "CoastingSpeed" "20" Option "CoastingFriction" "50" EndSection