Hello.

You can try any of the available force fields, as AMBER, CHARMM or GROMOS. GROMOS will be faster (as an United Atom FF) but AMBER and CHARMM are more accurate. For a successful MD, for 60-residue peptide, I would recomend no less than 5 ns for GROMOS and 10 to 20 ns for AMBER and GROMOS. But will also depend on the water topology, size of the solvating box and the protein itself (beta-sheet, helix, coil).

Best regards.