How can I change leaderboard stats to raise every 15 seconds from when the player joins?

I need help with changing this code so it raises 1 point every 15 seconds from when the player joins, not every 15 seconds the server is active and to make it so people in a certain group with a certain role will get a point raise, not guests:

amount = 1
timedelay = 15
currencyname = "Points"

while true do
	wait(timedelay)
	for i,v in pairs(game.Players:GetPlayers()) do
		if v:FindFirstChild("leaderstats") and v then
			v.leaderstats[currencyname].Value = v.leaderstats[currencyname].Value + amount
		end
	end
end

This is just the leaderstat script, it might not work though, it is for a rough of what it can be like:

local Lplayer = game.Players.Localplayer -- Find Local player
local LplayerLeaderstat = game.Lplayer.Leaderstat -- Get local leaderstat

while true do -- Loop every 15 seconds
  wait(15)
   LplayerLeaderstat.Points.Value = LplayerLeaderstat.Points.Value + 1 -- +1 point
end