On which field you want the dynamic LOV ?
One another way to populate the DFF (attribute15) is trigger.
Yes, that's possible.
For that, you need to create table Value set with Query for DFF
and then need to add the condition in Where clause of VS with using :BLOCK.FIELD pattern
Use Query as per your requirement in Table name of Value set,
(select distinct ship_to_org_id from oe_order_headers_all)
Where /Order By:
SHIP_TO_ORG_ID = :ORDER.SHIP_TO_ORG_ID
:ORDER is the Block of Order Management form and SHIP_TO_ORG_ID is one of the field, so you can filter like this.
I think Table Value set will work with DFF for this