Need faster reheating of frozen vacuum packed roast beef

That would almost certainly overcook the outside while leaving the inside still frozen, depending on how the package is shaped and the meat was originally cooked.

It takes time for the heat to penetrate the meat, which is why sous vide is classified as a "low and slow" method of cooking. Because your package is frozen, in order to bring the meat up to temp it has to thaw first, which takes even more time. Depending how thick the package is, if you pull it out in 15 minutes it is entirely possible that the inside will still be frozen.

If you cooked the meat sous vide in the first place, an merely wish to use 200 degree water to reheat it, you will over-cook at least the outside of the package, again depending on the size/thickness. If you cooked it in a more conventional way, its still possible that you will overcook it by using such a high temperature, as even chicken (which is usually cooked very well done) is only cooked to an internal temp of 165F.

Regardless, I would definitely expect some loss of quality if you reheat by boiling. In order to preserve the quality (tenderness, juiciness, flavor), your best bet is to reheat gently. Water temperature of 140F is generally recommended for reheating via sous vide. It will however still take time.

Is there anyway you could have the roast beef defrosted ahead of time? If so I would say that a stove top boil for 15 minutes wouldn't hurt the taste or quality much. If you have to go straight from frozen it would feasibly take like more than 15 minutes (depending on size). Now if you pre slice the roast beef before you freeze it and vacuum it in individual servings, dropping each serving in (even from frozen) to a stovetop boil would only take about 5 minutes to reheat properly, just slice thin and spear out evenly in each bag.