That would be in today's money $93.66 a week, or $2.34 an hour at 40 hours a week.
This web site, All about money | A Christmas Carol: The Scrooge Diaries , says:
"Half-a-crown – 12.5 cents
Shilling – 5 cents
Sixpence – 2.5 cents
Penny – Approximately half a cent
Farthing – Approximately one-tenth of a cent
So when the story mentions Bob’s salary of 15 shillings a week, you can easily see, even at that time, how measly it was. Mrs. Cratchit must have seriously splurged to buy those ribbons on her dress for sixpence. When A Christmas Carol was first published, it sold for 5 shillings a copy, cheaper than many books of the period, but still quite a luxury."
A Christmas Carol was published on 17 December 1843.
Reproduced from a c.1870s photographer frontispiece to Charles Dicken's A Christmas Carol (Photo credit: Wikipedia)
One Shilling GBP in 1850 had the purchasing power of about £3.80 GBP today, or $5.85.(from this site)
So, 15 shillings would be £3.80 x 15 = £57 a week, or $89.07. (from this site)
So he would make about $89 a week and $4628 a year, assuming he works every week of the year, which considering Scrooge won't easily let him off for Christmas he probably does work that much. I doubt very many families could support so many children on that amount. If he worked a 40 hour work week, that would be $2.23 an hour.