For any standard trip, airliners, best rate-of-climb (to your planned flight level) speed 105 KAS is the thing to do, the speed most efficient in gain of ground and fuel burn. Waning you’re passing 150 means you’re inefficient in your trip calculation, you’re too fast in dense air burning too much fuel, your gain of ground is not offsetting fuel burn, which is the most expensive part of your trip.
The 150 kts is prob to notify you are reaching top of maneuvering speed (abrupt leveling out could be considered a maneuver) which is abuse to the fuselage integrity against air density.