If the options listed in the previous answers are still too demanding, and the smartphone is really weak, then the task becomes more complicated. As the owner of the well-worn LG Optimus One P500, I often faced a similar problem.
If you do not consider a couple of already closed projects (there was a wonderful collectible game Spirit Stones, for example), then there are several options that have been tested on their own skin:
1. Retro Knights: 2048 is a fun pixelated analogue of the classic "2048". I was happy to kill time for her. 2. The Trader is a strategy, shop simulator. Google Play insisted that the application would work on my device, but the built-in memory was not enough. Perhaps someone will be more fortunate. 3. Space Trader is a port of an old toy. We fly, trade, fight. For a gray-haired smartphone, more than an interesting option, it killed a lot of time with it.
Earn to die 2. Interesting, long, not demanding hardware, works even on weak smartphones, and is free. The first part is for some reason for the money.
Some of the great games released a long time ago, 4-5 years ago, and therefore not at all demanding on the hardware:
Racing - NFS Shift, Reckless Racing HD, Reckless Getaway, Trial Xtreme 2, Earn to Die;
Puzzle - Where is My Water ?, The Room, Cut the Rope;
Other - Robotek, Jelly Defense, Samurai vs Zombie