Any help please?

hi…am trying to make destructible mesh …and getting very slow laggy performance when enabling gravity option its like slow motion …but when i disable it i get decent animation of fracturting it…any idea how to fix this ? what am doing wrong ?

here destructible mesh settings :

this without gravity

this with gravity on

i need gravity to do a simple explosion physics but for some reason its making performance so slow …how to fix it ?
thanks for any help !