Hi Fernando
US915 supports Spreading Factors SF7 through SF10.
The Spreading Factor is configured in the LoRa endpoint.
SF10 has a limitation of 11 Bytes payload, but provides longest range.
SF7, SF8, SF9 all provide larger payload. See Spreading Factor and Bandwidth
table at the link below.
http://www.multitech.net/developer/software/lora/introduction-to-lora/
-Best Regards