Population Density only changes the number of npc`s it has nothing to do with players or sessions. Everybody streams the world that surrounds them those with lower to minimum Density just have less traffic and npc`s around them. If you have the lowest setting and get near somebody with the max Density setting you will have the max Density too because his/her setting overwrites yours.
OP check your Nat Type if it`s "Strict" you will barely find any players in sessions. If you can`t or don`t want to get a Open Nat Type (Deactivated Firewall in Router) at least open these ports.
These have to be open for all Users! PC, PSN and Xbox Live.
GTA Online requires the following ports to be open:
TCP Ports: 80, 443.
UDP Ports: 6672, 61455, 61457, 61456, and 61458.
Xbox Live requires the following ports to be open: Xbox Only
Port 88 (UDP)
Port 3074 (UDP and TCP)
Port 53 (UDP and TCP)
Port 80 (TCP)
Port 500 (UDP)
Port 3544 (UDP)
Port 4500 (UDP)
All games published by SCEA (first-party) and the PlayStation Network may use the following ports for communication with SCEA (first-party) game servers: Playstation Only.
TCP Ports: 80, 443, 465, 983, 1935, 3478, 3479, 3480, 5223, and 10070 - 10080
UDP Ports: 3478, 3479, 3658, and 10070
If you don`t know how to do that google your router.
The best way to do this is with a Local Static IP Adress don`t use DHCP for P2P Games. You have to enter these Ports into your Router and link it to your Client (Your PC) with a Static Local IP Adress.
After you done that you will never lose connection to sessions and find much more players.
Here an example of my Local Static IP Adress.
IP Adress: 192.168.2.150
DNS Server: 18.104.22.168
DNS Server2: 22.214.171.124
You will have another Gateway the Gateway also shows the IP Adress for the most part their the same.
Just google it if you have no idea how it works.
All my Devices at home have Static IP Adresses.
This Site might help.