I think this was done to assure the games would be “Quick” rated and not take the remote chance that the games could end up with an e-time that would affect Standard USCF ratings. I could be wrong and would actually prefer a longer TC myself (like 25 10) but perhaps we would need to reduce the rounds. Please message BillScotty on ICC as he coordinates with the USCF and will have the answer.
A 15+10 wouldn’t ever count as a regular rated game according to that or any other posted/updated rules. It’s still quick, regardless of how much time is added via increment/moves.