Yes, hourly earning in the US is customarily gross earning (before taxes).

The median rule of hourly earnings to yearly earnings is 40 hours/week and 50 weeks/year, which results in every $1/hour == $2000/year in earnings.

For $15/hour, that's about $30,000. For a single person in California, without dependents and claiming themselves for one exemption, it would be 4,264.50 (14.22%) in Federal taxes and 579.35 (1.93%) in State taxes for a total of 4,843.85 (16.15%) in taxes.

Calculator: https://www.tax-brackets.org/californiataxtable