Banks requested 15% down for 3-units. Is that a Fannie Mae voilation?

[Olga Burninova]

Hello!

I'm looking for guidance/advice. 

I've applied for a conventional loan: 3 units, owner occupied, NJ, 5% down.

I have enough W2 income to cover the loan and additionally, there are two units rented already. 

Several banks said I have to put a 15% downpayment. 

Does it violate Fannie Mae guidelines? Are these guidelines enforceable? Or is it the bank's discretional decision to follow/not to follow FM guidelines? 

Thanks for any insights/suggestions in advance,