Ironically, slowing down delivery will de-congest the R/T traffic because it reduces the likelihood of repetition. Timely transmissions for big bites of climb/descent will eliminate those piece-meal transmissions for the sake of it. The knack is in creating spare R/T capacity. Caution with including three flight parameters in one transmission. I recall an incident report where an ATCO was criticised for giving a certain national flag-carrier height, heading and speed in one transmission. One of the three parameters was mis-selected, and the multi-crew opined that three in one transmission was too much to assimilate.