When bidding or estimating, you must always figure in where your last account is located. In this case, it is right in front of you! 32 acres? You are attempting to put a $$$$ amount on each acre.
Think about the fact that you 32 jobs @ one acre right in front of you. In other words you do not have to load your equipment 32 times for.
So, you must recalculate each acre accounting for the lack of fuel used to trailer, wear & tear on your trailer & truck, etc.
$15/hr? C'mon man, $40 per hour @ the very least needs to be figured in your calculations. At any and every lawn mowing account.
How long do you think it will take you to mow 32 acres? I mean if this is just you and another worker, you could be there for half a week.