"No cache" and "cache in memory" are the same thing, ie there is always caching, and the default is cache_in_memory; which explains why these two sets of figures are almost identical. But using caching will not improve speed; it's designed to reduce memory usage, but has a cost in speed.
If you know that your data is always iso-8859-1, then why do you need mb_detect_encoding()?
PHPExcel always expects data in UTF-8. If it were to be modified to accept any encoding, then it would still need to convert it to UTF-8 internally, so you'd just be transferring that work from your own script to PHPExcel; potentially with the added overhead of needing to determine whether a conversion was needed.
If you have an array of iso-8859-1 data and want to use the fromArray() method, then you might get some performance improvement by handling the conversion to UTF-8 within an array_walk() or array_walk_recursive() call rather than in a manual loop
If you know that your data is always iso-8859-1, then why do you need mb_detect_encoding()?
PHPExcel always expects data in UTF-8. If it were to be modified to accept any encoding, then it would still need to convert it to UTF-8 internally, so you'd just be transferring that work from your own script to PHPExcel; potentially with the added overhead of needing to determine whether a conversion was needed.
If you have an array of iso-8859-1 data and want to use the fromArray() method, then you might get some performance improvement by handling the conversion to UTF-8 within an array_walk() or array_walk_recursive() call rather than in a manual loop