Vibrations constrained to specific speed ranges are normally a balance issue; resonance.

However, 15-25 is also normally an 'acceleration" zone and vibrations during acceleration are often due to worn components (u-joints, cv axles, etc).

It's possible your stock CV axles were on their way out. When you swap the RCV's out put some new axles back in. Since you already replaced the front driveshaft that'll help rule out the worn components.