Love to help but
I am a CFI with at least 900 hours in the RV-4, however I don't think I will be able to help you directly. Are both you and the plane in the CO area?
The biggest challenge is no dual controls?
It sounds like you are a great candidate, but mention this only because it is not like a side by side. It will be a bit of an issue with any CFI. The good news a simple rear rudder peddle set-up and rear seat throttle extension is not hard to add, even a semi temporarily installation.
Access to the throttle and rudder are key. I would hate to be sitting in the back and have no control when a guy ground loops his new plane. So even if I could do it, I would hesitant because of this. No reflection on you or anyone, just I would not be effective as a safety pilot. Since you are really qualified as PIC, current, qualified, from a FAR stand point, you are PIC, so you don't need a CFI as far as the FAA cares. I understand the insurance aspect and it is a good idea. Are you insured for instruction during this 15 hour dual period? If so than the CFI will need controls for the insurance to be in effect. Other wise they might as well be on the ground and radio up instructions.
The 15 hours is a bit steep, but may reflect your tail wheel time. To learn to fly it and land should take 1/3 of this. The training is easy.
As a safety pilot/instructor I would not be able to help if things get out of hand. I would just be along for the ride. Hummmm. Like I said clips on the rudder cables for rear seater pedals and an extension shaft on the throttle (with a side quadrant) is easy to do. It would be goodness to add these. I had to when I got formation checked out. The safety pilot in the back seat of my RV-4 needed a throttle.
Giving "dual" would not be that hard, but without instruments it would also be a small challenge. Need help e-mail me.
G CFI/ATP