Neanderthal had average lifespan of 20 years, early Homo Sapiens had around 30 years, even modern human had average lifespan of around 30-40 years in medieval time. I think your civilisation probably reach Medieval Feudal level with nearly same speed like human civilisation, but it will be much harder for them to advance, because it requires practice - Malcolm Gladwell said you need at least 10.000 hours of practice to achive perfect result in anything. If your "halfing" works 40 hours per week, it will took him/her 10.000/40 = 250 weeks / ~5 years to advance to perfect results. Its unlikely, they will desire to spend 1/6 of their live on practice...
So, i think your halfing civilisation will reach Early Feudal level, with few Newton grade geniuses occasionally pushing them forward.
But, if their short lifespan is result of malnutrition and diseases, and it can be prolonged with proper food and medical assistance (at least to 50-60 years), they will probably advance as fast as humans do.
Also, if your civilisation respects book writers and do not burn books like various nazis do, it will be easier for them to learn and pass knowledge between generations.