Have you tried talking to them and finding the root cause of their delay?
Are they reading the cards every time?
Do they not know which cards are generally better than others?
Are they a generally indecisive person?
Addressing the root cause with suggestions might help, but it seems that the greater issue is that they don't seem to care.
If they don't care what the other players say, you need to have a one-on-one with them and explain that the JUDGE cares. Althought excessive time making choices in draft is not explicitly stated as a General Unwanted Behavior in the JAR, their behavior is disruptive to the tournament as a whole.
As a judge, the priority is to educate players who exhibit these behaviors. It can be useful to reinforce this
education with more stern penalties such as a Game Loss should the unwanted behaviour continue, especially
in cases where players are likely to upset others.
You can explain calmly and non-threateningly that if it continues to be a problem, you may have to take steps to penalize their continued slow drafting. Be prepared that this may upset them, and they may or may not come back. Either way, it sounds like you need the behavior to end.