Leveling system won't work properly?

I've been trying to create a leveling system using String Values. Basically, everytime you level up, you're given a new rank. E.g, Junior Manager, Manager, senior manager, etc.

game.Players.PlayerAdded:Connect(function(player)
	local rank = Instance.new('StringValue', player)
	rank.Name = 'Level'
	rank.Value = 'Cadet'
	rank.Parent = player
	
	local exp = Instance.new('IntValue', rank)
	exp.Name = 'Loyalty'
	exp.Value = 0
	
	local maxExp = Instance.new('IntValue', rank)
	maxExp.Name = "Max"
	maxExp.Value = 10
	
	
	exp.Changed:Connect(function(val)
		if exp.Value == 15 then
			rank.Value = 'Private First Class'
			exp.Value = 0
			maxExp.Value = 20
		elseif
		 exp.Value == 10 then
			rank.Value = 'Private'
			exp.Value = 0
			maxExp.Value = 15
		end
	end)
end)

Essentially, the problem is that the value changes to 15 like the bottom part of code asks, but it resets everytime when it reaches 10 instead of 15 like I want it to. Visual of error. Because of this, the text label will not change to say "Private First Class". I receive no errors in the output, and I'm completely stumped, any help would be appreciated.