Is there a way to make this copy script run faster without lagging the server?

I'm making a randomly generated Area by going through each location, and then recalculating chance. I'm using game:GetService("RunService").Heartbeat:wait() to slow down the script so it doesn't do it all at once and lag the server.

local player = game.Players.LocalPlayer
local rebirths = player.leaderstats.Rebirths.Value
local button = script.Parent
local Prefabs = game.ReplicatedStorage.Prefabs
local cubes = 90
local width = 100
local length = 50
local height = 6
local X = 0
local Y = 0
local Z = 0
local rows = 1
local w = 0
local l = 0
local h = 0
local chance = 0
math.randomseed(tick())

function DrawBlock(block, xp, yp, zp, location, num)
	if num == "" then
		local newBlock = Prefabs[block]:Clone()
		newBlock.Parent = location
		newBlock.Size = Vector3.new(3,3,3)
		newBlock.CFrame = CFrame.new(xp,yp,zp)
   else
		local newBlock = Prefabs[block]:Clone()
		newBlock.Parent = location
		newBlock.CFrame = CFrame.new(xp,yp,zp)
		newBlock.Size = Vector3.new(3,3,3)
	end
end

button.MouseButton1Click:connect(function()
	if player.TeamColor == BrickColor.new("Really blue") then
		local X = 148.95
		local Y = -102
		local Z = 615.84
while h ~= height do
		chance = math.random(100)/100
			if l == length then
				w = 0
				l = 0
				Z = 615.84
				X = 148.95
				Y = Y-3
				h = h+1
			elseif w == width then
				w = 0
				Z = Z-3
				X = 148.95
				l = l+1
			elseif chance<1 and chance>.85 then
				DrawBlock("Iron",X,Y,Z,workspace.ReallyBlueBase,"")
				w = w+1
				X = X-3

			elseif chance<.84 and chance>.74 then
				DrawBlock("Coal",X,Y,Z,workspace.ReallyBlueBase,"")
				w = w+1
				X = X-3
			else
				DrawBlock("Stone",X,Y,Z,workspace.ReallyBlueBase,"")
				w = w+1
				X = X-3
			end
	game:GetService("RunService").Heartbeat:wait()
		end
	end
end)

Thanks in advance!