Maybe it is jsut the way you try to process this values which makes it slow, you could try somthing different like in this post.
So my idea would be to distribute the received value to an other item and then you can process this items with a other rule. You can then put all e.g. all voltages into one group and have a rule triggered by this group to process the value.
Not tested but something like this.
rule "433MHz RX"
when
Item MQTT_Trigger_Dummy changed
then
// keep upper values, remove lower part only
switch Integer.parseInt(triggeringItem.state) & 0xfffC000 {
...
// only send lower values to item to update.
case 150000: Sensor_volt_1.postUpdate(triggeringItem.state & 0x3fff )
case 130000: Sensor_temp_1.postUpdate(triggeringItem.state & 0x3fff )
case 110000: Sensor_hum_1.postUpdate(triggeringItem.state & 0x3fff )
...
}
end