Yes, 9v9 with 15 on the roster might be ok. 7v7 is definitely too much.
I would ask:
- What league(s) are you playing in
- How many on the field for that league (7v7 or 9v9)
- How do you sub
- Do you blend with other teams (have some of your teams players play on another team, or have guest players join your team).
For question 1, some clubs may be playing in multiple leagues. Like maybe an outdoor game on saturdays and a indoor or futsal game on sundays.
For question 4, this would be the one I would be concerned about. If they shuffle players around, that is a mess and would be a no-go for me. You don't get that team cohesiveness and a host of other problems. Alphaforms does that and its horrible. As far as other clubs doing that, its not really a club thing as much as two coaches getting together and doing that.... or a coach having multiple teams.