I gave this task to IT technician, he has tried to get this info over the phone, 1st support level (students) were not able to provide info, so they have transfered him to 2nd support level (Iskon technicians) they can change mode to Bridge, and tell you PPPoE password, your PPPoE username should be the same one you use for moj.iskon.hr
for other locations I did it over e-mail, just make sure your e-mail is registered in moj.iskon.hr as official contact (kontakt) e-mail address
I have tried FB 7490 <-> FB 7390 with WAN link 75/7,5Mbps on both sides, I am getting about 500-600kb/sec ~ 4Mbps with FritzBox IPSEC VPN tunnel, not bad, maybe it could go a bit faster, but I don't have FB on 10 or 100Mbit link
you should be able to saturate Iskon 5Mbps upload with your FB VPN