How long would it take to stop the Hail Mary?

hi! i've kinda put myself in a pickle trying to write a fanfic, and I was wondering if there are any people who know the math better than me who could help me figure out a way to work things out and make it plausible.

after a little bit of research i've come to understand that the Hail Mary travels at 1.5gs, or 94% of the speed of light. tried to calculate what that was in km/h and all i got was calculators for km/h*s and i have NO clue what that means. when i googled it i couldn't find anything either, big bummer.

anyway- my goal is to stop the ship mid transit between tau ceti and erid after rocky and grace intercept a radio signal on the way that they want to investigate. obviously i've run into the problem of how the hell they stop the hail mary before their planned destination on erid. is this even possible? have i put myself in a horrible position by planning things out this way?

pls help !! also ignore the whole "grace will probably starve to death if the trip is delayed any more" thing, i have a plan for that. thank you!!