Play with more than 3 friends?

[Patrick]

A party can only have 3 people, but can I join a server/dungeon with, say, 2 parties with 3 ppl each? I.e. could I play with max. 18 people together (in 6 parties) in one dungeon?

[Lowbei]

With 40kish people online on average, lobbies are forming within seconds, and they fill incredibly fast, so it is unlikely.

[limierr]

Statwise it is not possible. Have two team of 3 people together would be quite lucky already.
Also even if you reach 18 people in team in a 18 dungeons ... the number of portal will be lower than the number of player. so you will be stuck at some point.