The following relates to 14th rather than 15th century England. It's also from a work of popular history that shouldn't carry the same weight as scholarly research. That said, it may still be of interest to you.

Lordly status loosely correlates with income. In theory each earl should receive at least £ 1,000 from his estates. Most have between £ 700 and £ 3,000. The richest is Thomas of Lancaster, who has five earldoms and an income of about £ 11,000 in 1311. This is exceeded by only two people over the whole century . Second on the fourteenth-century “Rich List” is Queen Isabella, who allocates to herself 20,000 marks (£ 13,333) per year in 1327-30. First place goes to John of Gaunt, duke of Lancaster, whose gross income from his English and Welsh estates in 1394-95 is in the region of £ 12,000, in addition to a pension from Castile of about £ 6,600. Most barons have an income of between £ 300 and £ 700, but in a few exceptional cases— Lord Berkeley, for instance— a baron may receive as much as £ 1,300 per year.

Keeping in mind that the English Pound at this time literally corresponds to a pound of silver, a very heavy woman's weight in silver would be roughly the income expected of many 14th century Barons. A page after this there is a table that states that an Esquire or gentleman would have an expected income of £ 100 or more and that a middling merchant would have about £ 500 in capital. I think it's safe to say a heavy woman's weight in silver is quite a sum to all but the wealthiest of the elite, but not quite a vast fortune.

Mortimer, Ian. The Time Traveler's Guide to Medieval England: A Handbook for Visitors to the Fourteenth Century.

Others will have to confirm, but according to this website silver peaked in value in the 15th century being worth approximately 100 times what its worth today in 1477.

So if you marry a huge woman of say 100 kilos(to make the maths easy) the value would be about 3.8million pounds (thank you kind commenters for pointing out my glaring mistake) in todays value (source).

I think it's safe to say it would make you rich.

I think we are seeing from the responses here that the sum of money we are talking about is pretty substantial but it is worth noting that wealth in 15th Century England was defined qualitatively and quantitatively different than wealth today, particularly among the landed aristocracy.

Land is the key to wealth in a pre industrial society. A giant heap of silver is cash up front but the flow of taxes and the like from large land holdings so defines the structures of wealth and power in the middle ages that the hierarchy of both maintains the same nomenclature even today -- Duke of this and Prince of that etc.

In Imperial Russia (see how I nonchalantly moved the conversation across all of Europe like its no big deal?) prior to the freeing of the serfs, the people who worked the land, and by extension their productivity and the wealth it generated, changed hands as the land did. They were literally owned by the nobles who owned the land they worked.

These same structures don't apply universally but the systems of tax collection in much of Europe were influenced by the Roman systems that came before them. Landholders owed taxes to the crown and collected those taxes from their holdings, typically keeping whatever they could collect over and above what the sovereign demanded. (This is, incidentally, why governorships were so prized in the Roman period.)

So while a large pile of silver would make a man rich it could not make him wealthy. Absent the sophisticated structures of trade, investment, and capitol which were just beginning to emerge in Italy around the 15th century, true admission to the ruling classes required land and wealth was a product of that rather than (typically) a means to it.