Wouldn't want too many 9 minute losses in 150 nm, typical jet would be GS 200 +/- knots on descent...be fun from the north in winter with a 100 kt jet stream
Let's look at the numbers then?
150nm / Tas 470kts = 19 mins average speeds not accounting for descent.
To save 9 mins would require a G/S of 320kts.
You could probably reduce speed at cruise alt and save a 1 min maybe 2 and reduce descent speed to save a couple more BUT a I would descend immediately to 20,000 at flight idle normal speed to get down ASAP and at min speed have a TAS of around 320kts or slightly slower. That with a slower descent and you have saved your 9 mins. Unless your heading west you could assume a reduction in g/s due wind which als helps. It doesn't always work but 95% of the time it will with savings in fuel. I.e. More left in tanks for other reasons (weather etc)