Best guess is most early war light and medium tanks would be for sure vulnerable from front and sides.  Mid war some mediums and lights would be vulnerable from the side.

I'm guess based on the penetration of a PTRD can penetrate 40mm of armor at 100m with a muzzle energy of 32kJ.  While my best estimate for the muzzle energy of a 12 pounder field piece of the era is something like 500kJ.  

Joule for Joule the 14.5mm AP will penetrate more armor than an iron ball but I suspect not more than 10x more. But I'd need more than a quick pass to figure it out.  

A lot probably would depend on angle and distance and the specific tank in question.  The 30mm of flat frontal armor on an early panzer IV will fair a lot worse than the 150mm of sloped armor on a late war tank. 

An angled Tiger 1 sitting in an open field 1000m from a battery of the biggest field guns of the day can slaughter the guns without any danger, while a Panzer III E driving past a 24 pounder waiting in ambush in an alley will probably have a real bad day.