RE: OS FS 91 is it capable ?
For trainer type flight 10+ lbs for a 91 four stroke is very reasonable.
I built my son a trainer for his birthday and its powered by a magnum 91 4stroke. 60" long, 94" wingspan, 10.5+ lbs and it flies like a dream. Putts around at 1/4 throttle. Capable of nice loops and slow rolls. Its not an acrobat... but its not supposed to be. I think the airframe could easily handle several more pounds and fly well. Right now with a little headwind and lowered flaps it will almost stand still in the air at just above idle. I will eventually take the magnum 91 off for another project and will put a 72 in its place. I am sure it will still be plenty of power.
For trainer type flight I think it will be ok. 14.5 lbs is a little heavy but you have a high lift wing on that plane. If you are looking for a slow Sunday flyer I think you will be fine. If you want it a little sportier better look at a 2 stroke 91 or 4 stroke 120.
If you look in my profile gallery there are some pics of the trainer.