Is there a less laggy way I could change the color of multiple blocks in range?

So I'm trying to make a modified paint brush that has a size setting, and paints parts in range of the size when a part is pressed. Currently I'm using GetDescendants() and Magnitude to tell if a part is in range but it lags the game a bit. Wondering if there was any other way to do this without the lag? This is the part this concerns:

function setColor(part)
	local getDescendants = workspace:GetDescendants()
	if canSelectObject(part) and not db then
		db = true
		if brushType == "PaintBrush" then
		if inGui ~= true and inPalette ~= true then
		if eyeDropperImg2 ~= nil then eyeDropperImg2:Remove() end
		if script.Parent.area.Value == 1 then
			script.Parent.Color:FireServer(1,part,primaryColor.BackgroundColor)
		else
			script.Parent.Color:FireServer(1,part,primaryColor.BackgroundColor)
			for i,v in pairs (getDescendants) do
			if v.ClassName == "Part" and v.Locked == false or v.ClassName == "UnionOperation" and v.Locked == false then
			if v ~= part then
			if (part.Position - v.Position).magnitude < script.Parent.area.Value then
			if (v.BrickColor ~= primaryColor.BackgroundColor) then
				script.Parent.Color:FireServer(1, v, primaryColor.BackgroundColor)
			end
		end
		end
		end
		end
		end
		end