At 75 kg. (165 lbs.) you are in the light to middleweight sailor size category.
The Carve 151 may not have been a particularly good choice if you were
comfortable on your GO 155.
They have about the same volume, but the Go (what year model) 155 was probably a bit wider.
If you truly want to sail in 15-20 knots with your 5.5 and 6.6, a board in the 100-120 liter range
would most likely be better once you get used to it.
For 12-17 knots, on your 6.6 m2 sail, a Carve or Futura 111 would seem ideal.
If you get > 17 knots of wind real often, then your 5.5 and a Carve or Futura 101 would be a bit better.
You do not weigh enough to really get comfortable in > 15 knots of wind on a huge (for the conditions)
Can you sail the Carve 151 in this wind range....absolutely, but @ > 15 knots, the water starts getting choppy and rough, so you get a bumpy somewhat hard to control ride over the chop on your big board.
A smaller narrower board would handle the chop alot better.
There would definitely be a learning curve with the smaller board (a bit mmore tippy and more sensitive to your fore/aft position on the board, but you would figure that out pretty quickly.
Hope this helps,