What to do with different timings on the motherboard and memory module?

Question

laptops

Previously, the laptop had SKhynix 2GB 1Rx16 PC4-2400T-SC0-11, and it had timings of 17-17-17, after which a Kingston 4GB PC4-2400 module was bought with timings of 17-17-17, respectively, and everything seems to work, but since 8GB (4 soldered on the board) in total is nothing, it was decided to buy a bar for 8 or 16, however, when checking in AIDA64, it turned out that the laptop plows at a timing of 15-15-15.

There are two questions:

1. What timings should I replace the module with?

2. Although the laptop used to be stupid all the time (on SKhynix), how does this affect performance? Could he be stupid because of different timings?





UPD:
Screenshot of SPD -

Answer 1

1. You need to take with the same CL value (first digit)
2. Due to different timings, there should not be any special problems.