Am be putting in pre-order for 5. If it would be helping, I could be preordering another 10. Could also be picking up any units from first batch that pre-order person not taking.
All units from the first batch are already paid. You can try to contact the buyers to know if they are interested to sell their units.
If you are ready to pay for 15 units, place the pre-order. There is not a maximum limit of units to order the second batch.