Well, I'll give this a stab from what (I think) I've observed on this forum:
1-48 twist is not considered "fast", but it's faster than a 1-66 or so that are primarily designed for roundballs and shorter conicals. The 1-28 twists of many inlines are primarily designed for conicals and saboted bullets, which are usually longer. You are right in between.
I would say if the 155 grain is not giving good accuracy with various charges, try going to a heavier (therefore longer) bullet.
That's just my 2 cents. Wait for more replys, and if you edit your postand give thespecific gun you are using, it may help others give better advice.

IM jaybe