$15K is your moving expense.  "Gross-up" simply means the calculation of pre-tax income.

The way to think about imputed income:  your moving expense is $15k after tax, so you must have earned $26k, and paid $11k in taxes, to have this $15k after-tax money. 

$26k is includible in your gross income, and $15k is a deduction as moving expense.