How long should I try a new class?

I am a FFXI player from years ago and returning to after playing the PS4 beta and enjoying it.

How long do I have to play/try a class before I really get a feel for its mechanics and how it will feel? I played Conjurer to 15 and Gladiator to 10~. I was able to solo everything so far fairly easily.

Secondary question, when does getting into a party become useful? All the content I played through so far was not only soloable but having a partner or party would probably have been a hinderance rather than a help.

Thanks!

Kesei Steel
Maybe a Conjurer/White Mage

Party contents begins at level 15 with your first dungeon
As for mechanics, well it takes some times but you really get to enjoy the game once dungeons have started ^^

First, welcome to the game. There's a lot of differences from FFXI, especially in gameplay mechanics.

The game will introduce a gameplay-changing ability at levels 15, 30, and 50, following completion of a quest. The introduction of these abilities create the greatest changes to your skills and rotations. Generally though, after level 30, you will have a solid understanding of how the class works.

If you are asking if there is any content in the game you cannot handle solo, it is really only instanced content like dungeons, trials, and some FATEs with the equivalent of world bosses. Your first dungeons unlock at level 15 and are very rudimentary. They do get much more difficult starting from lvl 32 to 35, and there can be a few significant hurdles at lvl50 as well (Hard Mode, Coil, and Extreme Mode). Generally though, you will not need a static party outside of the dungeons to complete the story and run quests before level 50.