I've been using the dynamic VPN feature on my SRX a lot, but more for surfing the internet and less for accessing internal resources. I needed to transfer a 20GB file to my Synology and noticed it was only transferring between 2 and 4Mbps. When using the VPN to browse the internet, split tunneling is not used and all traffic travels back to the SRX and then is NAT'd and sent out the untrusted-zone. I can max out the connection speed when doing a speedtest.net test, but cannot get higher than 4Mbps when doing an iperf3 test end-to-end. Originally, I thought this was due to packet fragmentation so I lowered the TCP mss using "set security flow tcp-mss ipsec-vpn mss 1200" and that made no difference. When I'm home and inside the LAN, without the VPN enabled of course, iperf3 speeds on WiFi are a little over 600Mbps, which is great. I've removed the policer PROTECT-RE, but no change. Maybe I'm overlooking something, but I cannot understand why I'm seeing slow speeds when connected over VPN.
Model: SRX300
Junos: 18.4R3-S2
Configurations: HERE
JUNOS Software Release [18.4R3-S2]
SRX WAN: 1Gbps UP/DOWN
Remote Device: HP Laptop
OS: Windows 10 Home
WAN: 500Mbps UP/DOWN
Wireless Speed: 300Mbps UP/DOWN