I have been fortunate enough to have someone give me a Great Planes Super Sportster 60. Complete with TX, RX, batts. and engine. I still can't beleive it....

The Engine is an (apparently very dependant) Tiger something something.. .60. The owner was burning 15% (I think that means 15% nitro) fuel in it. I burn 10% in my Nexstars OS/FX .46
Is it OK to use 10% in the ol' Tigre. The reason I ask is that I remember reading something somewhere that said that you should never change the type of fuel you burn in an engine.

Is this just an Urban Legend?

Thanks in advance for your help,