I would think about an oil exchange and put in a synthetic 0W30 or 5W30. Personally I would go for the latter. I have my bias and it's Shell followed by Castrol, (knowing the chemistries intimately). Peugot will gravitate to Total (their recommendation - but they don't assure it as if they were to, it would have to be offered free within their service package. If you are just going for a top up, then use Total as that would have been its intial fill......the question is how clean is the oil on your dipstick.
Old oil (black and sticky) can serve to affect your petrol consumption by up to 15%........however synthetic oils should have far more engine life, the limiting issue being the gradual detrition in the additive chemistry (that goes with the base-oils that form the actual lubricant). Think of the additives as performing extra functionality like friction modification, sulphur removal, carbon removal, etc etc.