Duplicated membership options after updated to 5.15.1
It might not be a membership type but just a price list - if you go to Contributions - Manage Contribution Pages and then on the far right of the table click on Configure, one of the choices is Contribution Amounts. You might see these "-old" ones listed in there. Or if it is a real membership, it might be a price set which you'd see in the same place but on the Membership Settings instead of Contribution Amounts.