Looks like WHEEL_DELTA is defined for win and osx, but not linux. Retooling to utilize a $pref instead, as that will let the scroll speed be modifiable for any projects that need it.

Engine/source/windowManager/sdl/sdlWindow.cpp

@@ -434,7 +434,7 @@ void PlatformWindowSDL::_triggerMouseLocationNotify(const SDL_Event& evt)
 
 void PlatformWindowSDL::_triggerMouseWheelNotify(const SDL_Event& evt)
 {
-   wheelEvent.trigger(getWindowId(), 0, evt.wheel.x, evt.wheel.y * WHEEL_DELTA);
+   wheelEvent.trigger(getWindowId(), 0, evt.wheel.x, evt.wheel.y * Con::getIntVariable("$pref::Input::MouseWheelSpeed"));
 }
 
 void PlatformWindowSDL::_triggerMouseButtonNotify(const SDL_Event& event)

Templates/Empty/game/core/scripts/client/defaults.cs

@@ -41,6 +41,7 @@ $pref::Input::KeyboardEnabled = 1;
 $pref::Input::MouseEnabled = 1;
 $pref::Input::JoystickEnabled = 0;
 $pref::Input::KeyboardTurnSpeed = 0.1;
+$pref::Input::MouseWheelSpeed = 120;
 
 $sceneLighting::cacheSize = 20000;
 $sceneLighting::purgeMethod = "lastCreated";

Templates/Full/game/core/scripts/client/defaults.cs

@@ -41,6 +41,7 @@ $pref::Input::KeyboardEnabled = 1;
 $pref::Input::MouseEnabled = 1;
 $pref::Input::JoystickEnabled = 0;
 $pref::Input::KeyboardTurnSpeed = 0.1;
+$pref::Input::MouseWheelSpeed = 120;
 
 $sceneLighting::cacheSize = 20000;
 $sceneLighting::purgeMethod = "lastCreated";