If it is FTTN your best bet would be to wait until you have it hooked up and then the modem line stats can be checked to see whether it will be possible to reach those speeds before opting in for a speedboost.
If it is FTTN your best bet would be to wait until you have it hooked up and then the modem line stats can be checked to see whether it will be possible to reach those speeds before opting in for a speedboost.