This double jump script won't work?

I've been working on a platformer, but for some reason this script lags a lot in the server.

deb=false
J1=false
J2=false
mouse=script.Parent.Parent:GetMouse()

plyr=script.Parent.Parent

repeat wait() until plyr.Character
plyr.Character.Humanoid.WalkSpeed=24
local function onKeyDown( key )
    print("Key:", key, " Code:", string.byte(key))

if key==" " and plyr.Character.Torso.Velocity.Y~=0 and J1==true and plyr.Character.Humanoid.Jump==true and deb==false then
    deb=true
    plyr.Character.Torso.Velocity=Vector3.new(0,50,0)
    script.Sound:Play()
    J2=true
    wait(1.1)
    deb=false
end
end
mouse.KeyDown:connect(onKeyDown)

function D()
    if plyr.Character.Humanoid.Jump==true then
        J1=true
    end
end
plyr.Character.Humanoid.Changed:connect(D)

while wait() do
    if plyr.Character.Torso.Velocity.Y==0 then
        J1=false
    end
end

Help is appreciated.