CYVR was the scenery that made user realize memory is not infinite (on a 32 bit sim is *very* limited). The golden rule of optimization says that you should start working on the most memory-consuming items first, because they will give you the greatest benefits.
You already experienced that CYVR was never the cause of your OOMs (since you could use it with higher settings on non-PMDG planes) but of course, if you keep adding stuff, and you are already so close to memory exhaustion, you must lower something else.
Yes, of course lowering the CYVR texture resolution will help a bit (maybe you can sacrifice shadows, since P3D already have dynamic shadows), and the installer will give you an estimate of the memory savings. If this will cure your OOMs or not, it depends how much beyond the 32 memory limit you were: if you were just on the borderline, that might be just what you need, but you are out of a large amount, you must act on something else.