if its a good tyre with a stiff side wall they should be fine on a 15x6.5 rim..
you get more flex at the back due to the nature of how your using the tyre.
trust me a 165 on a 5.5" rim is not going to be stretched. 175 on a 7" rim isnt what i would call stretched either, its more a tight/undersized..
185/50R15 is prob a bit of an expensive size. just got the 195