Total Access Statistics is optimized to be extremely fast. For most calculations, it only requires one pass through your data to generate the results. Speed is mostly controlled by how fast it can read your data (imagine a recordset reading every record) and writing the results to the output table. The statistical calculations themselves are very fast once the data is retrieved.
In most cases, the performance is similar to a regular query. There are some calculations that require sorting (e.g. percentiles), which take a bit more time depending on the amount of data being analyzed.