Yes I am serious. It is higher for Mexican women who immigrate to the US , as those who come here tend to be from the rural poor (most of Mexico's population is now urbanized). However, the problem will take care of itself as 1. Mexico's birthrate is rapidly falling, as is the case with ANY urbanized society and 2. Second and Third generation Mexican Americans tend to have birthrates closer to the American median.
The truth is that birthrates are falling all over the world, with mostly only the Africans these days having high birthrates, a fact mitigated by the high rate of infant mortality in subsaharan Africa.