Yup it exists. Exactly the same as Fifa 14 from my experience so far. Opponents outrun my defenders who can't seem to move and score from improbable angles whereas Bale shoots wide on a one on one with the keeper. Last night's stats had me with 17 shots of which 13 were on target. The opponent had 4 shots with 2 on target. I lost 2-0.
Unfortunately, at least to my knowledge, there is no Online Career Mode for FIFA 15, nor have there been in any previous FIFA installments.
There are however a couple of Online (PvP) modes that support co-operative play. One of which is Pro Clubs, in which, you and a number of friends create a team. The players in this team comprise of AI and Virtual Pros (which is basically a player you create). In this game mode you take on other people's teams in an attempt to reach Division 1. You can also compete in cup events that happen once or twice a month.
The other game mode is Co-Op Seasons, in which you and a friend (I think this is limited to one other player only, not sure though) play as any team on the game, and you play against another co-op team playing as another team. The aim is the same as Pro Clubs, in which you try and reach Div 1, along with the optional cup windows.
In both game modes, Matchmaking is customised according to what Division your team is in; so people in Div 10 wont be put against people in Div 3 for example. And in Co-Op Seasons, Matchmaking is also calculated against the team you select's star rating; so you won't get Accrington Stanley vs Barcelona for example.
More information on Pro Clubs and Co-Op Seasons
Best Answer
Simple answer: you can't
Ever since FIFA 13 (I think), you have not been able to practice with your pro in the arena. This happened when EA decided to separate the offline and online virtual pros as people were playing offline with friends and boosting.
The only real way to "practice" is to play games with your pro.
Online: either Drop-In matches or Pro Clubs games.
Offline: progressing through your career