Is the $15k pre tax?
It depends what you want to do.
I have $15k allowance - works out to roughly a $45k car, over 3 years, fully maintained.
You can up the price of the car if you lessen the amount of support services. I have fuel, rego, insurance, tyres, servicing and RACV - you can opt-out of any of these items)
Note that as of this year, the best deal combines some pre and post tax earnings. Ends up costing you (take home) about $10k a year - so you effectively save $5k