How to reduce 'PathFindingService' lag?

Hey. I am making a zombie game (with waves) in which I want to use the PathFindingService, but when the number of zombies on the map becomes more than 25, they start to stop due to a delay. Can anyone help me with this?

spawn(function()
	while vars.Wandering.Value == false and human.Health > 0 do	
		local desgx, desgz = hroot.Position.x+math.random(-WanderX,WanderX), hroot.Position.z+math.random(-WanderZ,WanderZ)
		local function checkw(t)
			local ci = 3
			if ci > #t then
				ci = 3
			end
			if t[ci] == nil and ci < #t then
				repeat ci = ci + 1 wait() until t[ci] ~= nil
				return Vector3.new(1,0,0) + t[ci]
			else
				ci = 3
				return t[ci]
			end
		end
		
		path = pfs:FindPathAsync(hroot.Position, Vector3.new(desgx, 0, desgz))
		waypoint = path:GetWaypoints()
		local connection;
		
		local direct = Vector3.FromNormalId(Enum.NormalId.Front)
		local ncf = hroot.CFrame * CFrame.new(direct)
		direct = ncf.p.unit
		local rootr = Ray.new(hroot.Position, direct)
		local phit, ppos = game.Workspace:FindPartOnRay(rootr, hroot)
		
		if path and waypoint or checkw(waypoint) then
			if checkw(waypoint) ~= nil and checkw(waypoint).Action == Enum.PathWaypointAction.Walk then
				human:MoveTo( checkw(waypoint).Position )
				human.Jump = false
			elseif checkw(waypoint) ~= nil and not checkw(waypoint).Action == Enum.PathWaypointAction.Walk then
				human:MoveTo( checkw(waypoint).Position )
				human.Jump = false
			end
			
			if checkw(waypoint) ~= nil and checkw(waypoint).Action == Enum.PathWaypointAction.Jump then
				connection = human.Changed:connect(function()
					human.Jump = true
				end)
				human:MoveTo( waypoint[4].Position )
			else
				human.Jump = false
			end
			
			if connection then
				connection:Disconnect()
			end
			
		else
			for i = 3, #waypoint do
				human:MoveTo( waypoint[i].Position )	
			end
		end
		wait(math.random(4,6))
	end
end)

while wait() do
	local nrstt = GetTorso(hroot.Position)
	if nrstt ~= nil and human.Health > 0 then -- if player detected	
		local function checkw(t)
			local ci = 3
			if ci > #t then
				ci = 3
			end
			if t[ci] == nil and ci < #t then
				repeat ci = ci + 1 wait() until t[ci] ~= nil
				return Vector3.new(1,0,0) + t[ci]
			else
				ci = 3
				return t[ci]
			end
		end
		
		path = pfs:FindPathAsync(hroot.Position, nrstt.Position)
		waypoint = path:GetWaypoints()
		local connection;
		
		local direct = Vector3.FromNormalId(Enum.NormalId.Front)
		local ncf = hroot.CFrame * CFrame.new(direct)
		direct = ncf.p.unit
		local rootr = Ray.new(hroot.Position, direct)
		local phit, ppos = game.Workspace:FindPartOnRay(rootr, hroot)
		
		if path and waypoint or checkw(waypoint) then
			if checkw(waypoint) ~= nil and checkw(waypoint).Action == Enum.PathWaypointAction.Walk then
				human:MoveTo( checkw(waypoint).Position )
				human.Jump = false
			end
			
			if checkw(waypoint) ~= nil and checkw(waypoint).Action == Enum.PathWaypointAction.Jump then
				connection = human.Changed:connect(function()
					human.Jump = true
				end)
				human:MoveTo( waypoint[4].Position )
			else
				human.Jump = false
			end
			
			hroot.Touched:connect(function(p)
				local bodypartnames = GetPlayersBodyParts(nrstt)
				if p:IsA'Part' and not p.Name == bodypartnames and phit and phit.Name ~= bodypartnames and phit:IsA'Part' and rootr:Distance(phit.Position) < 5 then
					connection = human.Changed:connect(function()
						human.Jump = true
					end)
				else
					human.Jump = false
				end
			end)
			
			if connection then
				connection:Disconnect()
			end
			
		else
			for i = 3, #waypoint do
				human:MoveTo( waypoint[i].Position )	
			end
		end
		path = nil
		waypoint = nil
	elseif nrstt == nil then -- if player not detected
		CchaseName = nil
		path = nil
		waypoint = nil
		human.MoveToFinished:Wait()
	end
end

Since you didnt provide your code, im assuming your using: while wait() do pathfinding code end

wait() defaults to like .12999 seconds or something. Very small. Zombies dont need to update that often. Instead, I suggest doing:

while wait(2) do
	pathfinding code
end

This won't make a huge difference because the zombie is still moving, yet it will drastically reduce lag.