Late fee laws in Maine

[Brett Jones]

So as I understand it, in the state of Maine a tenant needs to be 15 days past due on rent for it to be considered "late" before a late fee can be added to the rent. 

https://ptla.org/rights-maine-renters-paying-rent

What I'm unsure of is if this is for a Tenant at Will only, or if the tenant has signed a lease with a different arrangement, does the lease apply?

Any guidance from a Maine property manager would be appreciated. Thanks.