Went to the local Hobby Shop to pay my dues and join the local r/c club. Asked for a gallon of 10%, got it, paid for it, got it home, and it's 15%. Will this do harm when breaking in a O.S. 65 LA??

If you don't mind paying a little more for 15%, it will be fine in your LA.

Dr.1

you'll be fine... as menitoned.. it just cost a bit more

If you paid for 10% and got a 15%... then you got yourself a bargain [:-] unless of course you're a nice man and you go to the hobby shop and pay the difference

You'll be fine. I don't know if you paid for 10% or 15% but the difference is small. A little more attention is in order next time I guess. LHS employees are not noted for their "rocket science" degrees. Keep an eye on them at all times whenever you buy anything.

Scooter,
My OS 46 LA won't fly on 10%.
My altitude is around 2,000 feet above sea level.
You may have been saved from a lot of headaches.
Good Luck,
KW_Counter

Check your breakin instructions. Mine (diff engine) said to breakin w/ 5% and run w/ 5~15%.
G