MXF files have a built-in index which results in data being read in precise fragments with minimal overhead and the reading is nearly always sequential.

MPG (TS) files don't have an index, they have timestamps instead, which need to be located within the file. This results in jumping back and forth and reading larger chunks of data (with overhead to locate the timestamp), so it will always be significantly slower than MXF.

As the low proxying speed in the customer configuration may be associated with reading from the network storage, for further improvement of the proxying speed Cinegy recommends looking into its configuration and performance (e.g., to check whether file cashing has been enabled which may contribute to reading performance, etc.).