Huge Feature Class load slowly in Arcmap & Server

i have big layer of LV electrical lines (~1.2 million records)
If the layer is stored in a filegeodatabse or SDE, it loads very slow in arcmap or in the web application (takes around 10 s to display all features)
- i tried to recalculate the index nothing changed
- create new index again nothing changed
- minimize the number of fields

if i export the layer to shapefile it loads very fast (2 s) in ArcMap

any feedback on the above?