You don't post your location, so I don't know if your "150K" is km or miles. However, if it's miles, you waited even longer than I would have (so much for 'frequent'), and it's when the tranny fluid is left far too long that the old adage about changing the fluid appears to have some merit, at least on an anecdotal basis. Apart from that particular condition, I know of no mechanic who specifically recommends leaving in part of the old fluid for any reason. Even 150K Km would be too long for some owners' use models.
And yet I return to the previous question: "Do you believe it is possible to perform those services TOO frequently, or is more better? When there are less subjective means for determining a good service interval, why not employ them?"