The fowllowing should do the trick. Though there is no guarantee that it will be faster than creating the model in JuMP.
const MPB=MathProgBase # shorthand for long module name
"This function takes an optional solver and loades a model from an LP file "
model=buildlp([-1,0],[2 1],'<',1.5, solver) # create dummy model with correct solver
MPB.loadproblem!(model,filename) # load what we actually want
lp = loadLP("file.lp")