Something I discovered recently, for my tiny Go Lambda functions it is basically always worth it to run them at least with 256mb of memory even if they don't need more than 128mb. This is because most of my functions run twice as fast at 256mb than they do at 128mb. Since lambda pricing is memory_limit times execution time, you get better performance for free.

Test your lambda functions in different configurations to see if the optimal setting is different than the minimal setting.