For protein-RNA complex, amber ff14SB works good, but am not sure if this forcefield will be ok to use for a disordered protein complex. Pl. suggest the optimum choice of forcefield and the duration upto which the system should be simulated.
There is no 'perfect forcefield' . And simulation time depends on many parameters such as your interest of the problem and your computational resources.
@Sarath Chandra Dantu, even i have read about ff14SB force field to work on nucleic acid but i am not sure if i can use it for an IDP, as they are more flexible than structured protein.