It sounds like you need a calculation that splits off the final two characters of your dimension field. This would give you a separation of year and week. Here's how I mocked it up:

• Created an excel spreadsheet with a column labeled Week and rows ranging from 201501-201652, turning around from 201552 to 201601, and a column labeled Sales with randomized data for each row
• Connected to the spreadsheet in Tableau
• Converted the Week field from numeric to string
• Created a calculation field called Year that reads like this:     LEFT([Week], 4)
• Created a calculation field called WeekNumber that reads like this:    RIGHT([Week], 2)
• Switching over to Sheet 1, drag WeekNumber onto Year to create a hierarchy
• Drag the "Year, Week" hierarchy to the Rows shelf, and Sales to the Columns shelf

Now you can drill in and explore your data!  Let me know if this helps.