My Follow mouse r15 version not working at all?

hello, I found an error on your script: you forgot the () on

local UpperTorso = Character:WaitForChild'UpperTorso'

Modified script: (Worked on my test)

local Player = game.Players.LocalPlayer
local Character = Player.Character or Player.CharacterAdded:wait() ; Character = Player.Character
local UpperTorso = Character:WaitForChild('UpperTorso')
local Neck = UpperTorso:WaitForChild("Neck")
local LeftHand = UpperTorso:WaitForChild("Left Hand")
local RightHand = UpperTorso:WaitForChild("Right Hand")
local Humanoid = Character:WaitForChild("Humanoid")
Humanoid.AutoRotate = false
local HMR = Character:WaitForChild("HumanoidRootPart")

local Mouse = Player:GetMouse()

local RC0 = CFrame.new(1, .5, 0, 0, 0, 1, 0, 1, 0, -1, 0, 0)
local RC1 = CFrame.new(-.5, .5, 0, 0, 0, 1, 0, 1, 0, -1, 0, 0)

local LC0 = CFrame.new(-1, .5, 0, 0, 0, -1, 0, 1, 0, 1, 0, 0)
local LC1 = CFrame.new(.5, .5, 0, 0, 0, -1, 0, 1, 0, 1, 0, 0)

local NeckC0 = Neck.C0
local NeckC1 = Neck.C1

game:GetService("RunService").RenderStepped:connect(function()
    local cf = workspace.CurrentCamera.CFrame.lookVector.Y

    local Kek = CFrame.Angles(0, 0, math.asin(Mouse.Origin.lookVector.Y))
    RightHand.C1 = RC1 * Kek:inverse()
    LeftHand.C1 = LC1 * Kek

    Neck.C0 = NeckC0 * CFrame.Angles(math.asin(Mouse.Origin.lookVector.Y), 0, 0):inverse()
    HMR.CFrame = CFrame.new(HMR.Position, Vector3.new(Mouse.Hit.p.x, HMR.Position.Y, Mouse.Hit.p.z))
end)

I didn't understood what exactaly you want with this script, so it can not be what you're expecting, next time, explain a little better =D

Good Luck With your games!