That makes sense, Tom. When you increase the memory setting, you also gain more CPU power.

Lambda allocates CPU power linearly in proportion to the amount of memory configured. At 1,792 MB, a function has the equivalent of one full vCPU (one vCPU-second of credits per second).

Have a look at this aws-lambda-power-tuning tool. It’s goal is to help optimise the memory setting for cost, speed, or a balance between the two.