It's slightly roundabout, but I've done this in ModelBuilder with success (although I am using the same method to create a constant raster):
First, create an empty .dbf (table) in your directory (using ArcCatalog). Next, add a new column and call it 'value' (or whatever metric you are using). Enter however many values you need. The OID column will auto-populate, but we can ignore that.
Save your edits to the table, and in ModelBuilder, set it up in the iterator in the following way:
The multivalue iterator isn't what you're looking for. When you add an iterator, select the 'Row selection' option. Next, input the table you just made, and in the 'Group By Fields' section, select the 'value' (or whatever you called it) column. Link the table and the value to the raster calculator.
Lastly, in the raster calculator, you'll want to divide the raster by '%Value%', since that value changes (check the link below for inline substitution to read about how this works). You'll probably want to change the file outputs, or they will be overwritten each time. Maybe something like "Land_%Value%". If you run with 10, 15, and 20, you'll get outputs of Land_10, Land_15, and Land_20.
Inline variable substitution