As @billg mentions, there are often hardware differences between North American and “rest of the world” variants. If the only hardware difference is lack of Band 12 compatibility (I haven’t closely examined the specs), in theory, then H1512 would function on Republic’s network minus access to Extended Range LTE from a hardware standpoint.
The challenge is the software build on the phone. In addition to model number, Republic’s 3.0 app verifies that an appropriate software build for North American factory unlocked phones is present. Again, in theory, if one were to obtain then flash an appropriate North American software build, Republic’s app might see your phones as being compatible.
Please understand I’m neither encouraging or discouraging your from looking into this possibility further. That’s your decision to make but know there’s no guarantee that flashing the appropriate firmware will work, particularly if hardware differences beyond lack of Band 12 capability exist. As this is outside the scope of typical support, Republic will not help with this.
If I wanted to investigate further, I’d ask here: Android Forum for Mobile Phones, Tablets, Watches & Android App Development - XDA Forums. Or, perhaps, our friend @bitflung will drop in on the conversation?