Hi there,
The VTF15H is a well respected sub, but it's a considerably different design from the ML Depth you're used to (a large ported box vs a smaller sealed box). I'd suggest for a more apples to apples comparison looking at the ULS-15 from Hsu. Some other worthwhile contenders in that class would be the PSA XS-15 (or XS-30), Rythmik F15HP, and the SVS SB13-Ultra.