to Tortola you will be going dead against the trade
winds and current
all the way. Strength varies a lot that time of year but 15-20 kts would not be unusual.
In March you may still see periodic cold fronts coming in from the north that often reverse the easterly trades and can give you a boost on your course. Just be careful the front doesn't bring stronger winds than you expect and don't get caught in the Gulf Stream
in a norther.
You can beat your head
against the weather
, go non stop and get there in a 10-14 days with any luck. Or you can take your time, island hop, enjoy the trip and take a couple of months.