Levels help but their impact is much smaller than food or gear. If you have very low bow skill that might get tedious, thats one skill where levels matter.

As for troll itself. Its succeptible to pierce damage, so arrows of coruse. But also spears and daggers. Meleeing Trolls is a daunting task, but you can learn their attacks and dodge (or parry with bronze blucker).

When playing single player remember to always look at terrain you are going through and how many enemies are there. 1v1 on known terrain is always easy. But trolls hitting stuff make noise which brings more enemies from afar, so get him to chase you to a safer spot first then fight.

ps: Bows are easy, but there are cases where you'll be presented with close quarter fight with troll later, if you want to win that, train in open area first.