Inspiron 15 3000 3585 | RAM Upgrade runs slower than stock & supposed clocks, can't OC in BIOS.

I received my Inspiron 3585 last week. Ordered 2x8GB G.SKill F4-2666C9D-16GRS to swap the stock 1x4Gb 2666Mhz coming with the laptop (which was Hynix HMA851S6CRJ6N). 

The new RAM is dected (16GB) in the BIOS and on Windows, but the BIOS runs it at 2400Mhz instead of 2666Mhz. There doesn't seem to be a way for me to set the clocks and speeds manually.

How can I make the RAM run as fast as the stock ram did (and as fast as it is supposed to be running) ? It's quite important to me as the laptop is running on a Ryzen CPU and is used to render videos everyday ( the 5% performance gap I can get will save me hours over the year).

Thanks in advance, 

Jeff