Hello Bikas ji.
I would suggest that you use local transportation that are available from Kathmandu to Pokhara/Beni, Beni to Tatopani/Ghasa, Ghasa to Jomsom, and then Jomsom to Muktinath.
OR,
If you are thinking of taking your R15 up to Muktinath, then i would suggest not to take your R15...