I think Marseille are more likely than Lens to finish the season at the second position in the standings. The point gap is quite close now and I won't be surprised if Marseille get ahead of them in the near future. Marseille have a much better squad before anything else. They are able to show this by their performance these days as well. They are still on a nice winning streak.
Lens still beat them by 1-0 away before though but I think the scenario could be different when they play against each other again. Marseille have a really good team effort now and the Troyes game was one of the good examples for it.
Currently, Marseille can focus more on Ligue 1 competence after being eliminated from the Champions League. Marseille had experienced difficult weeks, after playing matches with a busy schedule. Plus, some of the players are exhausted, also, some are injured. in the second half of this season, Marseille progressed with three wins which left Igor Tudor's army only two points apart from 2nd place in the standings, Lens. therefore, Marseille has the potential to return to second place in the Ligue 1 standings, especially if Lens slips in the following matches.
IMO, Marseille has better depth than Lens, and Igor Tudor's squad should be able to boost their players to perform with stable performance.
On the other hand, Lens also have matches that should be easy for them in the next few weeks. it's just that, I quite doubt they will still appear with a very stable performance. at its peak, Lens has a game against Marseille, also has matches against other tough teams like visiting PSG headquarters. for sure, Lens will find it difficult to maintain their ranking on the Ligue 1 standings.