You can check the timeframe for processing E-2 visa applications in the US, by accessing https://egov.uscis.gov/cris/processTimesDisplayInit.do.
At the bottom of the page you will see the California Service Center in the drop-down menu. To the right of that is Service Center Processing Dates. There is a chart with the I-129 for E-Treaty Traders and Investors Processing Timeframe.
If the number of months is listed, that means that the Center is meeting its goal for processing Form I-129 for E-2 visas. However, if the Center is behind in processing the applications, a filing date of the last case completed will be listed. The dates are updated around the 15th day of each month. The average processing time is two months, however, that can change depending on the workload of the Center.