Index it to inflation and cost of living.
But in any event $15 everywhere in the US regardless of where you live...that's an insane policy.
The USA is way too diverse economically for a uniform minimum wage. I recall reading somewhere that it takes $100k in Manhattan to replicate a $38k lifestyle in some low cost parts of the country.
$7.65 nationally is way too low and $15 is probably fine in major metros like NYC, LA and the Bay area. The issue is lower cost areas. I'd guess something like $10-13 is an adequate balance in most of the country, between supporting workers and avoiding businesses switch to capital to avoid overpriced labour