So My reel says I can 12# mono but I want to use 15# fluorocarbon since it doesn’t stretch, is that ok? 

It’s ok, to use heavier line. That number on the reel just shows how much line will fit. But, don’t believe that fluorocarbon line doesn’t stretch. That, is a myth.

Ok thanks for the advice

1 hour ago, Anthony509 said:

So My reel says I can 12# mono but I want to use 15# fluorocarbon since it doesn’t stretch, is that ok? 

You will be fine.  I find fluorocarbon to be significantly more sensitive than monofilament.

I use mono for treble hooks and fluoro for single hooks.

 

You can use any size line you desire.  The only penalty you will pay is less line capacity,  but let's be serious,  does anyone need more than 70 yards for bass?

 

Don't believe the "pros,"  fluorocarbon has tons of stretch. 

15# fc is generally the same diameter as 12# mono. that's not always the case though.

 

i'm with the other folks that have posted, fc does stretch. i use it because of the sink rate, i feel i stay in contact with the bait better.

4 hours ago, roadwarrior said:

You will be fine.  I find fluorocarbon to be significantly more sensitive than monofilament.

 

?

Only restating what has already been said, the information about the spool is to only inform about capacity, it is not a suggested limit for line size.   FC does stretch, it just does so much differently than nylon mono.

I wouldn't use 15 lb FC on a standard bass size spinning reel, 8 lb is better choice.

Tom

OP never stated if the reel was a spinning or casting reel.  Do not put 15# fluoro on a spinning reel it'll fly off like a slinky.  Like Tom said 8lb is the absolute max you want to go on a spinning reel if you want to use fluoro.