RAM Upgrade

Yes, those are compatible memory for your Dell G15, however, it may not advisable for upgrade as it's a 16 GB kit (2x8GB) and your system has 2 SODIMM slots total.  You may not be able to use the existing memory.

@Chino de Oro​  yes i know im planning on removing my 1 8gb stick to replace it with the 2 other 8gb sticks, would this still be advisable?

I suggest to order just a single module of 8 GB and with your existing stick, you will have total of 16 GB.  The memory in your link is compatible with your G15. 

@Chino de Oro​Does it need to be the same brand or model?

Not necessary, same specification within JEDEC should work.  The memory from your link has the same specifications of Dell RAM https://www.dell.com/support/manuals/en-us/g-series-15-5520-laptop/dell-g15-5520-setup-and-specifications/memory?guid=guid-e9d2ea83-38a4-431d-803c-96d63c1dbc34&lang=en-us

@Chino de Oro​  So this should be the right purchase for me ? 

https://www.scorptec.com.au/product/memory/ddr5-laptop-memory/104490-ct8g48c40s5

Yes, that is a compatible one.  I verified the part number CT8G48C40S5 using Crucial compatible tool here.