I would wait until last minute, and probably it would cost you a lot less than 2.5k
#buying bp with 150 Points
junior patrol
If today was the last day I would say yes 2.5k is worth it.
But you can save a lot more GE with being a bit more patient
You can easily get one level every day doing the dailies + a special on avarage every 2 days
For me the easiest special is killing planes in GRB, if you are lucky you can get even 3-5 special done in one day
10 levels for me would be probably a week.
There is still plenty time to grind those levels
Just try to avoid specials like killing 60 mediums and such
Those can take very long
Just generally avoid "kill certain type" missions, its annoying to rely on gaijin matchmaking
The ones which you need to use a type of vechicle are good though.
SPAA is my favourite, thats the leas kill required and u can speedrun that with 2.7 Sweden
For the "kill planes" I use 5.0 Italy
The absolute best is "kill 1 plane in every game" for 4 matches
You just have to kill a plane in the match and go to the next one
Good luck!
Hope you can join to the Zuni Zuni club soon