How can i make the npc look at the player while walking?

so im making a enemy ai, and i need it to look at the player at all costs, so when i try to move him while he is looking at the player he laggs alot and can barely walk

i have this code:

while wait() do
NPC:SetPrimaryPartCFrame(CFrame.new(NPC.PrimaryPart.Position,Player.Torso.Position))
end

along with the classic follow script with some modifications, so, how can i make the npc stop lagging when walking

Theres some free models that can do this but if you want to know you can use also you can look at one of the free models scripts place it at npc model and it should work

CFrame.LookAt(NpcPosition,Lookatposition)

local Players = game:GetService("Players")


------------------ [[ Cofigurations ]] ------------------

local LookAtPlayerRange = 25 -- Studs between player and dummy that dummy can look.

-- [Head, Torso, HumanoidRootPart], "Torso" and "UpperTorso" works with both R6 and R15.
-- Also make sure to not misspell it.
local PartToLookAt = "Head" -- Where should the npc look at.


local LookBackOnNil = true -- Should the npc look at where they should when player is out of range.

--[[
	[Horizontal and Vertical limits for head and body tracking.]
	Setting to 0 negates tracking, setting to 1 is normal tracking, and setting to anything higher than 1 goes past real life head/body rotation capabilities.
--]]
local HeadHorFactor = 1
local HeadVertFactor = 0.7
local BodyHorFactor = 0.6
local BodyVertFactor = 0.6

-- Don't set this above 1, it will cause glitchy behaviour.
local UpdateSpeed = 0.3 -- How fast the body will rotates.
local UpdateDelay = 0.05 -- How fast the heartbeat will update.

-------------------------------------------------------



--
local Ang = CFrame.Angles
local aTan = math.atan
--
--------------------------------------------
local Body = script.Parent

local Head = Body:WaitForChild("Head")
local Hum = Body:WaitForChild("Humanoid")
local Core = Body:WaitForChild("HumanoidRootPart")
local IsR6 = (Hum.RigType.Value==0)
local Trso = (IsR6 and Body:WaitForChild("Torso")) or Body:WaitForChild("UpperTorso")
local Neck = (IsR6 and Trso:WaitForChild("Neck")) or Head:WaitForChild("Neck")	
local Waist = (not IsR6 and Trso:WaitForChild("Waist"))

local NeckOrgnC0 = Neck.C0
local WaistOrgnC0 = (not IsR6 and Waist.C0)
--------------------------------------------


-- Necessery Functions

local function getClosestPlayer() -- Get the closest player in the range.
	local closest_player, closest_distance = nil, LookAtPlayerRange
	for i, player in pairs(workspace:GetChildren()) do
		if player:FindFirstChild("Humanoid") and player ~= Body and Players:GetPlayerFromCharacter(player) then
			local distance = (Core.Position - player.PrimaryPart.Position).Magnitude
			if distance < closest_distance then
				closest_player = player
				closest_distance = distance
			end
		end
	end
	return closest_player
end

local function rWait(n) -- Fix many heartbeat lag issue
	n = n or 0.05
	local startTime = os.clock()

	while os.clock() - startTime < n do
		game:GetService("RunService").Heartbeat:Wait()
	end
end

local ErrorPart = nil
local function GetValidPartToLookAt(Char, bodypart)
	local pHum = Char:FindFirstChild("Humanoid")
	if not Char and pHum then return nil end
	local pIsR6 = (pHum.RigType.Value==0)
	local ValidPart
	if bodypart == "Torso" or bodypart == "UpperTorso" then
		if pIsR6 then ValidPart = Char:FindFirstChild("Torso") else ValidPart = Char:FindFirstChild("UpperTorso") end
	else ValidPart = Char:FindFirstChild(bodypart) end
	if ValidPart then return ValidPart else
		if ErrorPart ~= bodypart then
			warn(Body.Name.." can't find part to look: "..tostring(bodypart))
			ErrorPart = bodypart
		end
		return nil end
end

local function LookAt(NeckC0, WaistC0)
	if not IsR6 then
		Neck.C0 = Neck.C0:lerp(NeckC0, UpdateSpeed/2)
		Waist.C0 = Waist.C0:lerp(WaistC0, UpdateSpeed/2)
	else
		Neck.C0 = Neck.C0:lerp(NeckC0, UpdateSpeed/2)
	end
end

--------------------------------------------

game:GetService("RunService").Heartbeat:Connect(function()
	rWait(UpdateDelay)
	local TrsoLV = Trso.CFrame.lookVector
	local HdPos = Head.CFrame.p
	local player = getClosestPlayer()
	local LookAtPart
	if IsR6 and Neck or Neck and Waist then
		if player then
			LookAtPart = GetValidPartToLookAt(player, PartToLookAt)
			if LookAtPart then
				local Dist = nil;
				local Diff = nil;
				local is_in_front = Core.CFrame:ToObjectSpace(LookAtPart.CFrame).Z < 0
				if is_in_front then
					Dist = (Head.CFrame.p-LookAtPart.CFrame.p).magnitude
					Diff = Head.CFrame.Y-LookAtPart.CFrame.Y
					
					if not IsR6 then
						LookAt(NeckOrgnC0*Ang(-(aTan(Diff/Dist)*HeadVertFactor), (((HdPos-LookAtPart.CFrame.p).Unit):Cross(TrsoLV)).Y*HeadHorFactor, 0), 
							WaistOrgnC0*Ang(-(aTan(Diff/Dist)*BodyVertFactor), (((HdPos-LookAtPart.CFrame.p).Unit):Cross(TrsoLV)).Y*BodyHorFactor, 0))
					else	
						LookAt(NeckOrgnC0*Ang((aTan(Diff/Dist)*HeadVertFactor), 0, (((HdPos-LookAtPart.CFrame.p).Unit):Cross(TrsoLV)).Y*HeadHorFactor))
					end
				elseif LookBackOnNil then
					LookAt(NeckOrgnC0, WaistOrgnC0)
				end
			end
		end
	end
end)