The Early Termination Fee is just like you read. It's $400 for the first 90 days, then $15 less each month thereafter. The contract is for 24 months.
The problem is you're working it down to the last month having an ETF of $15. It doesn't. The 24th month's Early Termination Fee would be something like $85. After that 24th month the contract is over, and you can cancel with no ETF.
Edit: I forgot to add that only the reps can tell you the exact amount for your ETF right now, but it's most likely somewhere around $265.