Realistically, we need to win with this count. Needing 19 points, we need quadruple runs, or a triple with a good bit of peggjng.
Throwing 55: A or 2 gives us 16 points, needing to peg 3. 3 gives us 15, needing to peg 4.
Throwing A2: 4 gives us 18 points, needing to peg 1.
The first gives 6 or 8 cards to get us close. The second gives us 4 cards to almost certainly win.
If we can estimate (can we?) that pegging 3 is about the same as 4, and that either is about half as likely as pegging 1 or 2: both plays give us the same chance of winning. Otoh, keeping the smaller cards gives you a slightly larger chance of 3/4; but keeping the larger cards, you need only 1, which is almost a sure thing.