I am considering installing a YS 110 in my GP GEE BEE, but I am wondering how it will perform on lower nitro 15%. Will it still spin a 15-8 pretty good and idle decent, or do I need at least 20%.

YS engines generally like higher nitro. I know a flyer or two who use lower nitro, but you pay for it with a more finicky engine. They also like lower amounts of (or better, none) castor. 20-30% nitro is what the importer recommends. The standard is YS 20/20.

Take it from a non-expert who has learned from experience, 20/20 is the way to go. My 91fz ran fine wide open on 15% but was frustratingly finicky at part throttle til I switched to 20%. Don't understand why, but it just DID.

You bought a high performance motor, so it might not be a good idea to cheap out on fuel. It's kinda like using 87 octane gas in a Vette or Ferrari engine. The 110 and all other YS 4-strokes run best on 20% nitro or above. All three of mine like Powermaster YS 20/20 fuel:

Jez, why would anyone have that many small YS engines?